Arouse the DAMPFHAMMER!
Only one half is needed, as exhaust valve opens at BDC and only at scavenging phase, where exhaust cam closes, intake cam opens the valves, both cams are near to the piston. No need to rotate twice, it even can insult the measurement if the liner touch after squeezing the clay shift it's position. One half rotation is just enough.Yes, I carried out 2 full rotations to cover both intake and exhaust.
Anyway, seems your measurement saw the smallest possible distance of Piston and Valves. Good. Seems to be you see what it is. Really surprising high.