Will sameTime allow a day fighter to attack an enemy at lower altitude or do I need to choose between sameTime or lowerAltitude?
Yes, it means what you would expect. Same time (should -- if it doesn't I'll have to correct it) allow a unit on map 0 or 1 to react to the trigger unit on map 0 or 1. If the unit is on map 2, it can only react to a trigger unit on map 2.
The canReactFunction will search all the possible map combinations (all, sameTime, lowerAltitude, etc.) trying to find a match, and return true when it finds one.
I am loving this by the way. It allows for such differentiation between types of units. For example I believe the below means (given that I've created the table for alliedFighters) that the 190s will "react to" or intercept Allied bombers while the 109s will react to or intercept Allied fighters, giving each another reason to be built. The Ta152 will react to everything. Is this understanding correct?
Yes, that is correct. Keep in mind that allAir is every single air unit (any unit with domain 1), including munitions. That doesn't necessarily matter (since munitions aren't k-units and can't therefore trigger a reaction), but just something to keep in mind, since I mostly made it as a quick and easy way to get a large set of units. Incidentally, making an 'area' reaction against munitions only could be an indirect way to increase survivability of a certain unit.
Also, by changing "range" it would change how far away a triggering unit could be for the unit to react - so if I wanted to, the 109G6 might have a range of 1, the 109G14 a range of 2, and the K4 a range of 3 - making each unit much more useful despite having the same ammo?
Yes, that is correct. You probably want any air unit that can defend a strategic target against bombers to have a range of at least 2, since our air-protected stack 'fix' will be moving air units off those targets when a munition is created.
You will find that you have a good deal of customization of damage ability, when you get to setting up that part of the table (at least if you want to put a lot of work into making the tables). You could have a unit be really good at reacting to one kind of trigger unit, and do only little damage to another kind.