You’re on the right track. One thing you might be missing is that the value entered into the Materials Height slot is the difference between the top of the object to the top of where the tray would normally be. (So it has a maximum value of 0.5 ")
For your example, it would be 1.62" - 1.38" (top of the tray)=0.24"
You seem to have discovered most of these things for yourself, but there are several discussions, and quite a few methods for propping up materials to be engraved in the Free Files section. Folks have gotten very creative with everything to 3D printed and wooden props to bars that span the bed and 3/2/1 blocks.
I’ll link the calculator and a writeup or two with diagrams below so you can verify what you’re doing.
Be sure to check out the shared files in the Free Laser Designs section for the props.
