You put the wrong 40s enter in. Basic 40s support is R2 1.75 backspace, R3 1.25 tab, and R3 1.5 enter. You've already got a R3 1.75 control which can be used for physical compatibility for 12u/13u boards.
This is a pretty big oversight if kitting's finalised, as the R2 1.75 backspace is completely useless without a R3 1.5 enter.