well VV tghe simple answer to that is that Divine Rank is Based off in part by number of followers you have.... I do believe... I haven't really read over the entirety of the rules on this yet.. but I think that's a huge part of it.....
You won't find much information on the matter, because there are no rules for it. There are several options presented in Deities & Demigods, such as the power being inherent in the gods, power coming from followers/worshippers or a combination of the two, but these are merely suggestions with no rules attached to them.
But they could remain in our home planes/planets and that way we don't have to bother with the accounting of followers.
This. Or the power could be inherent in the gods, or partially tied to the world - as the world ages, the godlings increase in power automatically.
Of course, having to depend on worshippers could make things interesting in that promoting our religions would be important to the growth of our power. Tracking it, however, could prove to be rather onerous.
I suppose we could devise a system for how worshippers could impact divine rank if we wanted it to be that way.
Here is an example of how it could work:
Each person could grant a number of Belief Points:
Believer: 1
Worshipper: 5
Devotee: 10
Priest: 10*Level
Divine rank = SQUARE_ROOT(Belief Points) / 1,000
Tracking all of this could be quite tedious though. Some things could be approximated, but still. Say two religions declare wars on one another - how do you determine how many priests and devotees die from each? Or a godling decides to punish a city by smashing it turning it into a jungle (or blowing it up with a volcano, or whatever). Immediately you have to recalculate how many people died from what religion in order to reset divine ranks.