I am deeply interested by this thread and feature. I have Bubendorff roller shutter too.
for my side, the calibration has weird behaviour as well. during downward calibration movement, it stops the processs at approx 85%-90% of the full stroke, and for upward movement, it is same. At the end, the calibration passed, but in consequence, the travel stroke is not on the whole range.
I do not know if this behaviour is linked to my set-up, or if it is due to calibration process. ( done with light bulbs to simulate wattage measurement).