Serious PhysX question


I am trying to simulate a collision between two pendulums and compare with some experimental data:
Attached is what I got for the peak force:


Some offset can be adjusted, but I am not happy with the nolinear behavior of what PhysX gives me

Basically, as you can see, only in range of 10-40 kg they are not bad for my purpose.

Any tips???!!!

Some simulation settings:

FPS: fixed, 90 or 0.011 ms
Phys step: 1/30/16 = 0.002083333 ms
Sub steps: 16

CCD: ON on all colliding bodies

Solver Settings on each Rigid Body:
Custom Sleeping Threshold 1.0
Position Solver Iterations 8
Velocity Solver Iterations 2
Sleeping family sensitive