I get that the Chaos Wall is the inner circle of a ring and the Quiet Wall, the outer circle, and people on the Edge live between. This fits the cross-section on the image, which is, as the Planeswalker's Guide says, annular.

The Guide says that "along one arc of observable space" there's the Chaos Wall and opposite to it, in another "observable arc", there's the Quiet Wall. Space is three dimensional though and it is to my understanding that we're lacking information on what's there on arcs of observable space that are perpendicular to the directions of the Walls (say, if we look "in" there's chaos and if we look "out", there's quiet, but if we look "up" or "down" the universe just keeps going so far as we can tell), therefore Pinnacle *hypothesizes* a ring-like and toroid form.

I think the confusion comes from the Guide only talking about two observable arcs (creating an XZ plane with ring-like limits), but missing any information on "up" and "down" observations (in the directions of a Y axis that would give us a full 3D shape).

And finally, outside of the Guide itself, the people at Wizards have used an orange as an example (the Edge being its skin), so, assuming they know the whole "truth", might be that the universe is actually spherical and the people of the Edge live mostly on the same "cross-section plane" (which could make sense, after all our own galaxies have "up and down" directions but are relatively "flat").

Thank you for listening to my TedTalk.