I have a worse issue for you. The 40 is wide angle enlarging lens design designed to give a larger print without the head being so high. Typically they do not work well with condenser enlargers for reasons I do not understand. Mine do not work with any condenser machines without fall off & vignetting, yet they seem to be fine on a diffusion machine.
I have many of each type to experiment with.
All your assumptions in the original post are correct. The usual solution is a recessed lens board.