You're right, Arachnos, I thought you're speaking about the Abyss because it seems quite risky for a deity to live in an place where another (Asmodeus) has absolute power. It could happen to her what happened to Waukeen.
BTW, what is the relation between Asmodeus and the deities who live in Hell ? They answer to Asmodeus, perhaps, or they just tolerate each other ?
Well with the new
FR cosmology it aint a problem as all the gods seem to have 'acquired' their own planes to live on (which just happen to be identical, but seperate to where they were previously).
Lloth is the common example, she used to live on the 66th layer of the Abyss (the demonweb pits), but now in
FR (and backed up in book 5 of the Spider Queen series) she's up'd sticks and moved to the Plane of the Demonweb Pits.
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Before
FR messed up it's cosmology I'd assume that all the gods that made there homes in Baator got up to what they wanted to (which invariably means messing with the prime material), while they let the Big A do what he does best (which is rule hell)...
If i was playing a 3E campaign that used the old cosmology I'd give Asmodeus a (virtual) divine rank of 20 in hell (which would be enough to be all-powerful in his home, which is what he is).