@gip_86 I visited the IR-probe category, because I have made a magnetic flexplate with 1mm pertinax (phenol resin). It came sanded on one side from the vendor and because it's darker and opaque than FR4 it triggers the IR sensor well.
I had issues at first, because I powered the probe from 5V. With 3.3V it's much better.
Still my heightmaps look horrible, even when I remove the pertinax and probe the magnetic sheet instead.
Pertinax
height_pertinax.jpg
Mag-sheet only (with a glitch!, surface too shiny?)
height_magnetOnly.jpg
So it's either a not so flat mag-sheet (bought from a site for magnetic car advertising)
or the cast aluminum plate is bent...