The volume atmosphere in Poser is just a handy convenience for procedurally creating a bunch of planes and then applying a transparency shader on them that ignores normals and just uses the amount of light as input to the shader.

Well, you don't have to use that. You can use actual geometry.

Here I experimented with some parallel (with the ground) planes and a nice shader.

What do you think?

Oh, it is lit by one infinite but, being a prop, it can be lit by IDL.

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Renderosity forum reply notifications are wonky. If I read a follow-up in a thread, but I don't myself reply, then notifications no longer happen AT ALL on that thread. So if I seem to be ignoring a question, that's why. (Updated September 23, 2019)