Thanks for your replies!
@theruttmeister: Angling the probe could be a solution, I'll try that later!
Squares of blue tape is kinda impractical since I'd like to use mesh leveling and I use about 40 points... Also I can't live with the fact that the mesh then won't represent the exact surface. The curse of a perfectionist I guess...
@gtj0: I use it on a Duet WiFi which uses analog mode according to the website. Is there a way to switch to digital mode?
Yesterday I also found some weirdness in the readings of the probe which are displayed in the DWC as numbers from 0 to 1000:
Kapton on Blue Tape:
Z0.6-: 537 (triggered)
Z5.95+: 466 (possibly because of the surrounding blue tape, since I only used one strip of Kapton for testing purposes)
Kapton on Blue Tape after scuffing it up slightly:
Z0.65-: 537 (triggered)
Z0.7+: 466 (surface detected but not triggered)
Z2.2+: 0 (no surface detected)
Kapton on bare aluminium:
Z0.4-: 537 (triggered)
Z0.45+: 1000 (error)
Z0.8+: 466 (surface detected but not triggered)
("+" after a Z-value means "this Z-value and bigger")
So what this means is that when probing, the print head goes down (or the bed up in my case), then it senses the approaching surface (represented by a value of 466) but then it goes to 0 again. This leads to the error "probe wasn't triggered during probing move".
So a workaround could be to set the dive height to a very small height but that could be inaccurate since the time between slowing down and triggering is very short.