Thanks all for your help and suggestion.
I now know I shouldn’t take short-cuts.
I followed this tutorial Tutorial: How to cut without the Crumb Tray (Honeycomb) because I don’t have a digital caliper. After doing the math my tray is 35.5 mm tall. After adding extra material my total height is 36.4mm. So I set 0.9mm is 0.035" as my material thickness. And now my engraving is at the position I need it to be.
I’m not sure about the focal height. Does this influence the engraving dept?
I need to engrave about 1mm to add some inlay. I now increase the power making a lot of burn marks.