You can do some experimenting with it, but you might want to run a few test patches on whatever material you plan to use, to see what kinds of variances in shade you get by varying the settings.
(I ran a bunch of them, and eventually came to the conclusion that there wasn’t a heck of a lot of variation except between the extremes, so I just let the photo engrave do it’s thing for me…the results give more variation.)
I’ve got some small test strips in this post that don’t take all day to set up. They might be useful if you want to test the engraves on your material: