Depth of Calumet recessed lensboard

Can anyone give me the depth of a recessed lensboard for a 4 X 4 (CC-400) style Calumet board?
I am going to make one, I just need to know the distance of the recess. How far back is the lens moved by using the recessed board, as opposed to, a flat board?
Thanks-Matt

Looks like 1.25" on one that I have; the top of the recessed box is slanted down (to the rear) to clear the opening in the front standard when installing or removing the recessed board.