I believe i've seen the 3/4" model listed at 4.5" x 5"....but not 100% on that.
I agree on the 3 side viewing, can't wait to get mine setup. If you have the option to go pendant i'd probably do that and rig up something where you can adjust it for height over the tank. Then you could add a simple wood canopy that just slides on (Open on the back short side?) so it blocks the MH from blinding your room.
Are you going to be able to see into the fuge area? Or do you plan to paint that?