Can you control a distance field based height fog, with normal look ups and ramps?

Howdo All.
I am having some problems controlling my distance field volume fog.

Inspired by @Ryan Brucks and @Asher.Zhu, I have been working on a crypt scene with depth field based creeping fog, but the fog is also creeping up any nearby walls and the sides of the crypt.

My set up is:- Distance to object minus desired height of fog. I one minus this and then divide it by a soft edge value. This then gets multiplied by a noise and fed into the extinction value in the volume material

What I cant figure out is how the check against the vertex normals creating the distance field on the xy plane so i can multiply against them to control or reduce the field controlling the fog. I cant see where I would get the 3d value to query against.

I also would like to multiply the whole volume against a ramp volume made of texture ramps and normalised bounding box, so I can control the fade out of the volume better.

Any ideas?


using 4.25