I actually found the Baltic Birch plywood had a better dynamic range than the Proofgrade stuff. I have a thread on my experiments with engrave settings here:
https://community.glowforge.com/t/an-engineers-perspective-on-photo-engrave-settings-for-wood/15042?source_topic_id=16035Regardiing the masking: add a score on top of your cut line, then do a GFUI run with only the score enabled, then you can carefully peel off the masking (the score will have cut through it) without moving the material, then go back into GFUI and enable everything except the score before doing your final run.
This will allow you to remove the masking just over your piece. If you don’t mind the extra score line, you can alternatively do this just around your engraving area.