Two questions on preaching

[PvK]

I assume the preaching effects would be resolved in sequence, like other things seperate commanders do. That combined effect would already be pretty good.

There is something I don't quite understand going on with the effect of enemy dominion, though. I notice that provinces near enemy dominion have a lower level that "can't be raised any higher by preaching". My guess has been that every nation can have dominion in every province, and they subtract from each other somehow, in a slow process from turn to turn, and that dominion also slowly spreads from province to province. I don't particularly want to know all the details, since it is fun just seeing it be a bit unpredictable, but has someone explained how the dominions interact somewhere? Just curious.

PvK