A bit of an update on my 11x11 experience - I today started a large print that fills ~80% of the bed, and I did a cold 11x11 calibration of the bed before (@20°C bed temperature). This works nearly fine! The bottom ~1 cm of the print bed were too low and the print did not stick there, but adding pieces of cardboard between the bed and the frame for the front three bed screws was a quick fix to that (if not a sustainable one…). Now here’s a bit of first layer p*rn, bed at 60°C:
And this is my bed vizualisation (it is really a bad, bumpy bed!):
My conclusions:
a) 11x11 is good enough for my awfully bumpy bed, and the printer does a good job to compensate
b) Heated bed calibration not needed for me (the problem with the bottom centimetre would not have been fixed by this: this part of the bed is just not properly covered by the calibration).
c) I still need to do something about my bed - the first centimetre problem is real.