Somewhere is floating a pdf on dominion spread. Also KO commented on the matter at some point. Probably both can be found in that manual addenda that Liga was doing. You can't get that closer to the codex of the first ones, I think
Then there's the oral tradition... I bet if you made a thorought search you'd find all sorts of interesting stuff on the matter, and possibly even the two sources mentioned above.
Anyway, I think a priest's chance to get an increase on dominion is 10% times priest level. So, a level 4 inquisitor gets 80% in hostile dominion.