Thank you for the comprehensive report. Photos 5, 7 and 8 also provide some reasonable hope that the FP5 power and volume buttons (which are spread a bit more widely than their counterparts on the FP4) will most likely be all out in the open and fully accessible and usable in this case as well. Thanks for planning another FP5 in FP4 case test. 
Update @AndreasChris Fairphoner @JBap was hoping it was possible to wake up the display when lifting the flip case flap. I was wondering if an app like WaveUp (also available on the Play Store) could enable this. 
Perhaps if you find the time, you might want to try.