Stress/Force/Average - Problems

Hello,

I have problems with understanding a few commands:

The simulation issue is a box filled with particles where I want to analyse stress on different heights of the walls.

I use these commands

fix cad all mesh/gran/stressanalysis cube 1 1 0 0 0 0 0 0 finnie yes
fix GlobalforceOnMesh all ave/time 50 2 100 f_cad[1] f_cad[2] f_cad[3] file filename.txt
dumpstress all mash/gran/VTK 200 post/dumpCAD*.vtk stress wear cad

The manual says, that the fix mesh/gran/stressanalysis stores a global vector with 6 components, where the first 3 components are equal to the total force on the mesh in x-, y- and z-direction.

I have a primitive stl file for my box and I can visualize the pressure on the (in total 12) triangles in paraview.

1) What I don't understand is, if f_cad would calculate just a global force vector (3 scalars each timestep for the 3 directions of a 3d simulation), it shouldn't be possible for paraview to visualize the varying pressure on the two triangles of one of the y-walls of the box...

2) How can I access the forces on the mesh depending on the height of the box?

Thanks in advance,
kind regards,

Silias

P.S.: I assume, that it's not possible to calculate these force by looking at the per-atom forces, because they are equal zero, while the bulk material is more or less settled.