The +/- 0.05 (0.5 was wrong - sorry, will edit the original post) can even be avoided: In the calibration menu there’s “Sensor calibration” which seems to be exactly there for this purpose - you once manually calibrate both nozzles and the sensor offset is gone… This is however still a somewhat unprecise operation, but improved my setup now to 0/+0.05 mm L/R. I guess I’ll at some point do another one with something more precise than the calibration card, and taking more care than on first try.
Despite the botched start, I see development in the firmware - I guess in the end I’ll be happy!