What determines whether provinces can convert to the new pagan religion after reformation?

[SOSHaruhi101]

Playing Cosmopolitanism Hellenism and trying to min max how many provinces convert to my reformation at the very start. Can someone give me a full list of all the things that influence this in the current latest build of the game + all DLCs Thank you

 

[SOSHaruhi101]

Just did a bit of testing on Ck2. Seems like while all your vassals go Reformed_pagan when you reform, not all your provinces do. Trying to figure out if theres a way to guarentee certain or at least all provinces go reformed.