So for your case here you would pick somewhere like this on the base surface:


Then when selecting the target surface this would be the matching area that you would want to click on:


Note that you don't want to click right on the corner, it's a little bit away from the corner along one edge.

- Michael

thanks sir!! This helps a LOT; nowadays I literally make parts in ~2 hours from design > 3d print, Moi is a JOY to use!