I found this number on another forum post but it worked for me. Just add 0.022" (inch) to the surface that will be touching the base.
Here is the model and you can see where I “pulled’ some of the surface up 0.022” so the rounded edges will print as expected. I forgot to include the outside edges and you can see in the next image where those we slightly compressed compared to the inner rounds. It was printed upside down and directly on the base plate with no supports and turned out great.
Here is the final output from Form 2 with Std Grey at the lowest resolution.
This adapter is holding a magnifying lamp arm onto a tool cart I was customizing. It works really well with a few wood screws.