I wanted to use the sun and a little 5m cloud layer above my sphere using the noise driving my displacement as a shadow map, however, unfortunately this doesn't work, as the god-rays are culled within the area that is displaced, and only exist outside it.
It kinda seems like a bug, but I don't know.
I do have two spheres, one which has no shadows, and isn't visible to rays, and visible, this allows luminosity to work correctly visible without light interaction from the sun. The next sphere, is invisible, with no shadows, but is visible to other rays, and acts as the luminosity glow, and additive glow from the sun.
To me, the object surface not interacting with rays shouldn't affect cloud volumes.
PS, yeah I made sure it wasn't just the alt limits/depth of the cloud, and even overcomensated by 10km just to be sure. Lol