Hi Mat,
So here's the black cloud, and the shadow.
No gi, Direct Light Exposure : 1.67 (default is 0)
For the 4 zone I have : 4.7%, 17.8 %, 35.4 %, 72%
@density of the VDB is 0.15 (default 1)
I don't see any ray march quality or step length with VDB, only a quality in % for the Camera, reflection, refraction, shadow and GI.
All is set at 100% quality (default 50%)