So as promised here are my findings: Up until now I had the Clever3D PEI aluminium plate in natural color which is some kind of silver and as described in some post spread across some other threads I had issues getting a consistent Z height after homing. Using a feeler gauge to measure the distance between nozzle and plate after homing showed that it varied. Some times I had 10 times the same values then 5 times greater, then 3 times smaller. I tried homing with different lighting conditions and settings and I can tell so far that my LED lighting, external lighting, bed temperature have no influence on this. I didn't believe it really before but now I am confident that it is that way. With this plate the IR is totally dependent on the surface but has issues with that color it seems. So now I have a black Clever3D PEI aluminium plate available and did the same tests. I ran the same firmware and settings. And so far I can confirm that color matters! After roughly about 50 homing sequences I always get the same distance of the nozzle to the bed. That is with the IR sensor that came with the BB. Regarding the findings of @fpex who had problems with his blue sheet and better results with the red one I have no real explanation but I think I has something to do with the emission spectrum of those colors. Maybe blue absorbs too much of the infra red of the sensor.