I can’t contest your experience of course, nor the possibility that I need to calibrate
but this experience is a shared one from back in the day too
e.g. here
fwiw - I wasn’t using my ears alone, I was running an oscillator into the Ext Ins and comparing Cs across one octave, with the variable filter the tracking allowed pitch matching very accurately at either end, whereas the fixed filter was significantly off on that day in history
I use a vanilla patch, dial off the oscillator levels, add a teeny bit of noise to speed things up and set reso to full, then tune the filter to match an external sine osc in a middle octave range
I do recall the official line being that one filter was better at tracking than the other, keep in mind the tracking isn’t consistent across the whole freq range, so it may appear better in the sweetspot range for the LPF
Either way, I’m gonna give my machine a calibration soon to see if it corrects the disparity any 