First from last, get 1.40. 1.31 is buggy and bad. Interceptors indeed do wrong damage, 1-5 for lasers, 6 for MD, 2-7 for fusion. Dont think it was fixed anyplace, but most people doesnt even realize what interceptors not use PD and use normal beam values + some bonus instead.
Power of shield is for one shield face.
About explosions. They are mystery still as far i know. What i know for sure is what armor for fighters and missile class for eh, missiles really matter. But, area damage for missile stacks (here and later interceptors always included when "missile" is used) work other way than for ships. Weapons what do direct damage, say spatials or pulsars, or engine blast dont necessary hit missiles even if damage produced should allow it mathematically. There is some random element also, unlike beams. But, the weaker missile's armor\ stronger area damage is, the more probably you will wipe them off. Say you put many pulsars at ship, say 20 and shoot stack of 500 non-armored nuclear missiles. You will wipe them all outright, but with 3 pulsars, there is good chance you wouldnt. Sadly dont have a full answer here.
Idea is having all the mods in missile is reliability. Does you really need to put 3 more missiles on ship and take a risk of fail overall in case defence is slightly stronger than you supposed to be? What was the purpose of those 3 missiles if you lost due to them? In case you can know for sure the amount of defence you will encounter, you can skip some modes, but it essentially anti-AI exploit i mentioned. Surely its good if you can exploit it that way, its a skill too, but you also need to know the right way. Most important mod is fast, that one you better never skip. And about "non-armored non-dummy", dummies need to soak defence fire. They never can guarantee what you will hit anyway, so risk just dont pay off. Surely its not so noticeable with AI, coz it cant shot down missiles right way.
PD. The most important feature of pd is what they are single mod what can fire on auto on upcoming missiles. This mean what if your ship is hit pointblank with missileboat - single beam type what would work is PD. People who clain what they prefer normal beams just never played a real battle, so dont realize what effectiveness of normal beams vs AI missiles is just AI exploit. Nobody will use missiles so dumb as AI do, just shoot them at random ship and wait till defensive fleet will shot them all in united effort. But AI will do, and it so bad what if you play AI only you can never realize in your life what you simply play bad and do exploit instead of game. Next: +25% hit is really big stuff. At early game you cant hit from distance with normal beam anyway, suppose what you can hit from close one. But well, at same price you can have 2 PD and use them for same damage, but with aforementioned benefits and +25% BA. For long distance there is heavy beams. Also due to formula they also slightly more accurate than normal ones, thus making normal beams basically useless. And also, for late game you can get HighEnFocus. It will add +100% damage to PD but only +50% to normal beams. So at same size, 2 PD will do damage of 2 normal beams, and 1 normal only 1,5. The 2 things what bad with PD is indeed, range and shields. Thats why you also need Heavy mod, otherwise it would be useless too.
"But doing this over and over again is not really fun. Winning as soon as possible isn't the only way to play this game" As i got you didnt played many games yet, so you are in best game phase. When you can try different stuff etc. But good what you already get a good strategy. The problem is what the more you will play, the clearer you will see what by playing something looking different, in fact you essentially doing this over and over again. And even before you will start, you will know what you will win this game, just will spend more turns than you will using effective game strategy. After you tried all combinations of races and drop to win with antiraces like -food -prod feudal from prewarp - you will realize what trying to beat speed in game is in fact the single way to make a game at least somewhat harder, but ofc isnt not needed. Needed is understandment of game, what any other stuff you will do is the same blitz, just less effective. No matter if you use fighters and dont build any colony base and dont have autofacts and rlabs. Or you teched as creative some late tech and builded colonies. You still build some fleet what will win a game for you, usually using anti-AI exlpoits in process. Just in second way you will also do some unneeded steps, but they will result in same win, just on later turn. Ill throw an example what i hope will let to get it more easy. Suppose you win your usual game, teched to some beamX and eventually killed all AI's or Antares. But somebody saying "hey, its not all game, you just did some boring again and again blitz! You should leave one AI planet alive, tech all the tech, settle every planet, build all there and max pop. Winning as soon as possible isn't the only way to play this game!". Well. After you came to killing last planet of AI you know what you win already. Surely its nice to do described things once or 2 time. But after you did, there is no reason to do it every time, you already know what you will see in result. That that supposed guy mistake, if you dont do it now, maybe you did all that already. In example above is just added some redundant steps not needed at all to win a game. But some logic still lie in it, because basically unless you teched all the possible tech (till level 5 of advancedtech) and colonized every possible planet, and ALL of this PRE-war - you doing blitz, you spend a resources not on development, but on war. If you do it anyway - then there is no difference in doing it from start or add some redundant unneeded steps in process. Just doing it from start make game run effective, and adding redundancy doesnt add no real sense except of game exploration for new players and winning using suboptimal strategy. Problem what there is alotta suboptimal strategies, and its impossible to claim what some of them are better, or smarter or something else than another. They all are simply suboptimal, and can exists only VS AI, coz all they rely on anti-ai exploits and overall insane weakness of AI races, what let them survive and win, despite theyr poor performance. As another final example, suppose you play on tutor, and also using various cheats. But you doing it with different race designs, and claim what you "play game various ways" doing so. I guess its not so hard to get what in fact there is no "many ways to play this game" involved in this example.
Power of shield is for one shield face.
About explosions. They are mystery still as far i know. What i know for sure is what armor for fighters and missile class for eh, missiles really matter. But, area damage for missile stacks (here and later interceptors always included when "missile" is used) work other way than for ships. Weapons what do direct damage, say spatials or pulsars, or engine blast dont necessary hit missiles even if damage produced should allow it mathematically. There is some random element also, unlike beams. But, the weaker missile's armor\ stronger area damage is, the more probably you will wipe them off. Say you put many pulsars at ship, say 20 and shoot stack of 500 non-armored nuclear missiles. You will wipe them all outright, but with 3 pulsars, there is good chance you wouldnt. Sadly dont have a full answer here.
Idea is having all the mods in missile is reliability. Does you really need to put 3 more missiles on ship and take a risk of fail overall in case defence is slightly stronger than you supposed to be? What was the purpose of those 3 missiles if you lost due to them? In case you can know for sure the amount of defence you will encounter, you can skip some modes, but it essentially anti-AI exploit i mentioned. Surely its good if you can exploit it that way, its a skill too, but you also need to know the right way. Most important mod is fast, that one you better never skip. And about "non-armored non-dummy", dummies need to soak defence fire. They never can guarantee what you will hit anyway, so risk just dont pay off. Surely its not so noticeable with AI, coz it cant shot down missiles right way.
PD. The most important feature of pd is what they are single mod what can fire on auto on upcoming missiles. This mean what if your ship is hit pointblank with missileboat - single beam type what would work is PD. People who clain what they prefer normal beams just never played a real battle, so dont realize what effectiveness of normal beams vs AI missiles is just AI exploit. Nobody will use missiles so dumb as AI do, just shoot them at random ship and wait till defensive fleet will shot them all in united effort. But AI will do, and it so bad what if you play AI only you can never realize in your life what you simply play bad and do exploit instead of game. Next: +25% hit is really big stuff. At early game you cant hit from distance with normal beam anyway, suppose what you can hit from close one. But well, at same price you can have 2 PD and use them for same damage, but with aforementioned benefits and +25% BA. For long distance there is heavy beams. Also due to formula they also slightly more accurate than normal ones, thus making normal beams basically useless. And also, for late game you can get HighEnFocus. It will add +100% damage to PD but only +50% to normal beams. So at same size, 2 PD will do damage of 2 normal beams, and 1 normal only 1,5. The 2 things what bad with PD is indeed, range and shields. Thats why you also need Heavy mod, otherwise it would be useless too.
"But doing this over and over again is not really fun. Winning as soon as possible isn't the only way to play this game" As i got you didnt played many games yet, so you are in best game phase. When you can try different stuff etc. But good what you already get a good strategy. The problem is what the more you will play, the clearer you will see what by playing something looking different, in fact you essentially doing this over and over again. And even before you will start, you will know what you will win this game, just will spend more turns than you will using effective game strategy. After you tried all combinations of races and drop to win with antiraces like -food -prod feudal from prewarp - you will realize what trying to beat speed in game is in fact the single way to make a game at least somewhat harder, but ofc isnt not needed. Needed is understandment of game, what any other stuff you will do is the same blitz, just less effective. No matter if you use fighters and dont build any colony base and dont have autofacts and rlabs. Or you teched as creative some late tech and builded colonies. You still build some fleet what will win a game for you, usually using anti-AI exlpoits in process. Just in second way you will also do some unneeded steps, but they will result in same win, just on later turn. Ill throw an example what i hope will let to get it more easy. Suppose you win your usual game, teched to some beamX and eventually killed all AI's or Antares. But somebody saying "hey, its not all game, you just did some boring again and again blitz! You should leave one AI planet alive, tech all the tech, settle every planet, build all there and max pop. Winning as soon as possible isn't the only way to play this game!". Well. After you came to killing last planet of AI you know what you win already. Surely its nice to do described things once or 2 time. But after you did, there is no reason to do it every time, you already know what you will see in result. That that supposed guy mistake, if you dont do it now, maybe you did all that already. In example above is just added some redundant steps not needed at all to win a game. But some logic still lie in it, because basically unless you teched all the possible tech (till level 5 of advancedtech) and colonized every possible planet, and ALL of this PRE-war - you doing blitz, you spend a resources not on development, but on war. If you do it anyway - then there is no difference in doing it from start or add some redundant unneeded steps in process. Just doing it from start make game run effective, and adding redundancy doesnt add no real sense except of game exploration for new players and winning using suboptimal strategy. Problem what there is alotta suboptimal strategies, and its impossible to claim what some of them are better, or smarter or something else than another. They all are simply suboptimal, and can exists only VS AI, coz all they rely on anti-ai exploits and overall insane weakness of AI races, what let them survive and win, despite theyr poor performance. As another final example, suppose you play on tutor, and also using various cheats. But you doing it with different race designs, and claim what you "play game various ways" doing so. I guess its not so hard to get what in fact there is no "many ways to play this game" involved in this example.