When do I know I have enough agents in an enemy province?

[Z12LAZARUS]

Im trying to get a neighboring muslim province to rebel. (Im playing Spain btw)

I flooded this province with 9 bishops, but can I reach a point where sending more agents just wont do any more good?

Or can I theoretically send 100 bishops and 100 spies to a province and have all of them affect its loyalty?

[Urien]

I'm pretty sure that the more agents you send then the quicker this will affect an enemy provinces values. Loyalty (spies) and Religion (bishops, inquisitors, Cardinals). However, don't forget that your enemy can counter these effects with their own religious and political agents. Also, he can boost troop numbers which will increase loyalty in his province. Loyalty is also affected with the distance the province is from himself. Sometimes if he is camped in the province it will be almost impossible to get it to rebel, particulary if zeal is high.
Having a large amount of your agents inside an enemy province also leaves them open to enemy assassins too, particulary if that province has some protection such as watchtower or border fort.