Definitely you lose bellows extension if the lensboard is recessed, limiting the smaller size enlargements, however it might not matter to you, and you can always use the Setopla until you find a flat lensboard.

You also might be able to find a lens extender. 15 to 25 mm length should be OK. Nikon used to make these and I found a Canon RF threaded one (same 39mm threads), too.