The reflex mount I have in mind does not use the tapped holes for scope mounts. It uses the single screw that holds the existing rear sight in place. The rear of the mount slides into the milled recess at the rear of the existing sight slot that was used for the elevation screw.

Pistol scopes have much more 'mass' than reflex sights therefore should be securely mounted using all the drilled and tapped screw holes a handgun has available. Reflex sights are lower and lighter and the mount referred to above takes care of them quite readily, IMHO. .......