The big difference between the first, second and third renders. The lighting in Stratocumulus test 1.png with 75 million voxels is not showing much internal scattering, just a broad ambience, so I thought you would need to increase resolution in some way. But the latest 75 million voxel render is doing much better. It looks like some other settings changed, perhaps the density. If they didn't, then I don't really understand what's happening.
Matt