Having hard time with wpp and volume tools in fusion

Hello,
I really don't succeed in this.
I'm trying to use volume mask and/or volume fog with a world position pass from 3dsmax, and everything I tried failed, I followed tutorials step by step, I tried adding cameras from the 3dsmax scene, I also tried z to world pos tutorial, etc, etc, etc.

What I get is, either
- a bleeding mask with volume mask (i.e mask all over the place) or no mask at all (small white dot)
- or a black fog with volume fog,
- or world pos passes are all burnt out (white)
- z to world pos gives me a screen that is all blue (?!)
- I even go a weird masking that it was mirrored 4 times (in X and Y)
- (some examples posted)

Everything I'm doing doesn't do anything that is advertised in the tutorials, while I followed them millimeters by millimeters, re-checked dozens of times all the nodes. I even got help from somebody who tweaked my comp file and made it work and, amazingly, I tried to reproduce it while having it just beside, and it's not working in my comp (?).

Is there any special function to enable in a comp before working on it? Scale, units, frames, whatever?
Does anybody has a workflow tutorial in this regard?
Any help appreciated.

You're going to have to give us more to work with.

Whenever I read 3dsmax, the first thing that comes to mind is: have you accounted for the different coordinate system? Imported cameras will be converted by Fusion (Z-Up to Y-Up) but the world position pass won't. Here's a macro that does the conversion:

WPPConverter_v02.setting

never used the volume that much, so i skip on this

but the volume mask looks like you made the wpp channels wrong. it seems you copied the RGB color of the "beauty" image into the WPP channel and not the WPP channels itself