Izmir Stinger
Deity
I like the Wages of Sin scenario and it got me wondering why that sort of situation doesn't come up more often in a normal game. RoK/FoL's early and lasting dominance is one reason. They spread fast and furious and civilizations that wind up following one or the other have little reason to pursue another religion. Even when those two don't divide the world's faithful between them, most leaders seem content to switch to whatever religion reaches one of their cities first - no matter how out of character it is for them - and wind up sticking with it despite getting little benefit from it. I've made changes to several game files to tweak their behavior more to my liking. I've seen other people complain about this stuff, so I figured I'd share my tweaks with the community at large.
First, I dramatically lowered the passive spread rate of the various religions, especially the ones that can be founded early. That change is made in "[Fall from Heaven 2]\Assets\XML\Gameinfo\Civ4ReligionInfo.XML". If you aren't using any ModMods that modify this file (should only be those that change religions) you should just be able to overwrite your copy with this one. Otherwise you can manually edit it by reducing the number in "<iSpreadFactor>###</iSpreadFactor>" to a much lower value, or even 0 to prevent passive spread.
I have modified the XML file that defines the leader's characteristics and behavior. It already had some religious preferences built in for some leaders, but not nearly extreme enough to strongly encourage lore-appropriate religious choices. This one is at "[Fall from Heaven 2]\Assets\XML\Civilizations\CIV4LeaderHeadInfos.xml". For some of them I was unsure what weight to give them, like the Amurites. The original file had a slight weight towards FoL, and nothing else (Amurite FoL, really?). For the ones that weren't obvious, I just weighted them against ones that would change their alignment. Just overwrite your file with mine (rename it first) and you will see a more pronounced preference for appropriate religions and a decreased impetus to switch to a bad choice just cause it sneaked into their territory early.
Leaders that put a priority on founding a religion also tend to spread it to anyone they have open borders with, which is pretty much everybody that has cartography and isn't currently at war with them (or if they have cartography themselves, just everybody). Even with the weights, if there is no competing religion available, the one founded by the guy with open borders will inevitably get adopted. This is one of the main causes of the Sheaim not being AV. They may found it, but if every city already has OO or FoL, they will tend to stick with that. The problem is that the Sheaim leaders allow open borders even with civs they are annoyed with. I struggled with what to do about this problem and eventually decided the best solution was to make everyone require "Pleased" to sign an open borders agreement. This will also have the effect of further inflaming tensions in Erebus (a good thing in my book) because fewer open borders pacts means fewer "Our open borders have brought our people closer together" bonuses. It also means that civs of the same alignment are more likely to stick together, because the alignment diplo mod + "years of peace" should be enough to allow open borders with each other, but the alignment penalty will prevent it with others. Human players have the advantage of being able to play a game of Somnium if you really want an agreement (or just gift your map, in a pinch).
I made two different versions of this file, depending on how draconian you want to get with the restrictions on religious preference. The file called "CIV4LeaderHeadInfosOpenB.xml" has both my weighting and the restriction on open borders. "CIV4LeaderHeadInfosWeight.XML" just includes my weighting. Rename the one you want to use "CIV4LeaderHeadInfos.xml" and overwrite the existing file. These won't be compatible with any modmod that adds or changes leaders.
Another way religious behavior gets out of whack is the free disciples from lair exploration. Capria may strongly favor Order and strongly disfavor Ashen Veil, but if she has no religion currently and gets a Savant from a dungeon, guess who is going to be selling their soul to Hyborem? It also lets some random civ found a religion way before the civ that really cared about that religion can even research the tech for it. I decided to change the requirements for that lair event to having Priesthood rather than just Mysticism. If they have discovered priesthood and still haven't established a religion, maybe it is time they got one, even if it is random. This file is "[Fall from Heaven 2]\Assets\python\CustomFunctions.py". There is a bunch of stuff in there, and I don't expect this to be compatible with many modmods at all. If you want to manually change it, just search for the line "pPlayer.isHasTech(gc.getInfoTypeForString('TECH_MYSTICISM')):" and modify the tech to Priesthood or whatever.
I tested these, but it is always prudent to back up your files before overwriting them.
First, I dramatically lowered the passive spread rate of the various religions, especially the ones that can be founded early. That change is made in "[Fall from Heaven 2]\Assets\XML\Gameinfo\Civ4ReligionInfo.XML". If you aren't using any ModMods that modify this file (should only be those that change religions) you should just be able to overwrite your copy with this one. Otherwise you can manually edit it by reducing the number in "<iSpreadFactor>###</iSpreadFactor>" to a much lower value, or even 0 to prevent passive spread.
I have modified the XML file that defines the leader's characteristics and behavior. It already had some religious preferences built in for some leaders, but not nearly extreme enough to strongly encourage lore-appropriate religious choices. This one is at "[Fall from Heaven 2]\Assets\XML\Civilizations\CIV4LeaderHeadInfos.xml". For some of them I was unsure what weight to give them, like the Amurites. The original file had a slight weight towards FoL, and nothing else (Amurite FoL, really?). For the ones that weren't obvious, I just weighted them against ones that would change their alignment. Just overwrite your file with mine (rename it first) and you will see a more pronounced preference for appropriate religions and a decreased impetus to switch to a bad choice just cause it sneaked into their territory early.
Leaders that put a priority on founding a religion also tend to spread it to anyone they have open borders with, which is pretty much everybody that has cartography and isn't currently at war with them (or if they have cartography themselves, just everybody). Even with the weights, if there is no competing religion available, the one founded by the guy with open borders will inevitably get adopted. This is one of the main causes of the Sheaim not being AV. They may found it, but if every city already has OO or FoL, they will tend to stick with that. The problem is that the Sheaim leaders allow open borders even with civs they are annoyed with. I struggled with what to do about this problem and eventually decided the best solution was to make everyone require "Pleased" to sign an open borders agreement. This will also have the effect of further inflaming tensions in Erebus (a good thing in my book) because fewer open borders pacts means fewer "Our open borders have brought our people closer together" bonuses. It also means that civs of the same alignment are more likely to stick together, because the alignment diplo mod + "years of peace" should be enough to allow open borders with each other, but the alignment penalty will prevent it with others. Human players have the advantage of being able to play a game of Somnium if you really want an agreement (or just gift your map, in a pinch).
I made two different versions of this file, depending on how draconian you want to get with the restrictions on religious preference. The file called "CIV4LeaderHeadInfosOpenB.xml" has both my weighting and the restriction on open borders. "CIV4LeaderHeadInfosWeight.XML" just includes my weighting. Rename the one you want to use "CIV4LeaderHeadInfos.xml" and overwrite the existing file. These won't be compatible with any modmod that adds or changes leaders.
Another way religious behavior gets out of whack is the free disciples from lair exploration. Capria may strongly favor Order and strongly disfavor Ashen Veil, but if she has no religion currently and gets a Savant from a dungeon, guess who is going to be selling their soul to Hyborem? It also lets some random civ found a religion way before the civ that really cared about that religion can even research the tech for it. I decided to change the requirements for that lair event to having Priesthood rather than just Mysticism. If they have discovered priesthood and still haven't established a religion, maybe it is time they got one, even if it is random. This file is "[Fall from Heaven 2]\Assets\python\CustomFunctions.py". There is a bunch of stuff in there, and I don't expect this to be compatible with many modmods at all. If you want to manually change it, just search for the line "pPlayer.isHasTech(gc.getInfoTypeForString('TECH_MYSTICISM')):" and modify the tech to Priesthood or whatever.
I tested these, but it is always prudent to back up your files before overwriting them.