The universe is not a great wheel with planes shooting off like the gaps in the spokes. The simplicity and finity of the metaphor make that clear; rings are contained, restrained, and binding. And more, the idea that we can stand at the centre and look out upon creation from a position of authority is either willfully delusory or utterly naive. We are not at the centre but rather the bottom.
Look at the night sky in Sigil and you see stars. In Baator, stars. Celestia, stars, stars everywhere, separated from us by a dome of shadow. Or rather a sea, one which we can cross on golden ships to those bright points of light. After crossing the Nothing you find yourself at another plane, maybe one you recognise. You realise that this is true shape of things previously obscured my short lines and strange paths.
It is a sphere of shadows with orbs of light. This sphere is the bottom and the centre, yet most outer. Our physical intuition can't imagine the hyper dimensional spaces of the macroversal model.
Like an ant meeting a deer. On bumping into its hoof you perceive a great beast made of horn, towering in a neat column. This is hardly a fraction of the truth but the knowledge of it will suffice for your limited interactions with it. For that ant to become a great sorceror, shooting through the astral dark in a womb made of light, he would have to imagine legs and fur.
Imagine the ocean. The true god sits in a boat, sometimes throwing waste overboard, things unneeded and useless. They fall to the bottom of the ocean miles below in the darkness where life briefly blooms around it. Creatures fight and breed and live and die in the usual cycles of living things. The gods as we know them are whales, we feed on their corpses. Some of live by the thermal vents of the light universe above (below and inside), semi permanent sources of nourishment.
In all cases the nothing will settle, erode the shores it laps against. In some places the horizon knights rove back and forth, filling the nothing with something, but they cannot stop the tide.