How to test benefits of optical flow improvements

What does no better scaler mean? Anyone encounter such messages before?

Both FLOW_FnSCALER (PX4Flow) remain 0.

I repeat the calibration but both still remain zero. test performance drifts over 10mins.

[the drift was solved by putting back the default PSC_xx values]
PSC_POSXY_P
PSC_VELXY_D
PSC_VELXY_I
PSC_VELXY_P