[AreaOfEffect]

The overall point is that a prophet/heretic is best utilized on the fringes of your territory, mostly where the enemy has dominion.

If kept in your own lands the prophet's dominion spread will be hindered to a degree. The good news is that the two effects resolve separately. So a heretic and a normal prophet in the same zone won't effect your dominion any differently then prophet/heretic of the same heretic level.