I don't know the height answer but I do know with the 507k-x2 and standard height sights on a 365XL you do have barely enough to have 'irons'.

The rear of the optic has a built in rear notch. Figure out the height of standard sig 365XL front sights and that will be the minimum to get a backup sight picture.

It's small and not optimal, but definitely useable if ever needed.