Try looking to American Defense Manufacturing. I use one of their QD mounts on my Holosun HS507C-X2 on my 7.5" 5.56 pistol. Not the cheapest in the world, but VERY high quality.
ADM is proud to supply high quality AR Style firearms, mounts and accessories to law enforcement, military, competition, hunting, and recreational enthusiasts across the country.
Right now about 2 7/8 hob. Bottom of the dot front is about 1/2 from the rail, and the other mount pictured is "normal height" like used on an AR, it's about 5/16 to 3/8