Mm, yes I forgot exactly how this setup was working. So if you're looking at the whole scene through a very thin cloud layer you'll need higher quality for that layer and/or higher voxel scatter quality. But note that voxel scatter quality "mostly" affects noise levels in areas of, er, scattered light, so it *may* not be what's needed here. I'd increase cloud Ray Marching Quality to 2, and try Voxel Scatter at 400. It's definitely not a crazy value, in fact we raised the default to 100 a little while ago, and I'm tempted to raise it again...
- Oshyan