Softening or stiffening the high speed stack changes the damping force everywhere, not just a high speed.

The example below from the MXScandinavia thread on Thumper Talk replaces the 0.2 mm shims in the stack taper with stiffer 0.25 mm shims.

The dyno test results (data points) show the shim stack is stiffer everywhere across the speed range, not just at high speed. Shim ReStackor calculations (lines) show the same thing.

High speed stack stiffness has little influance on high speed damping force measured on the dyno