Lance's 225 gal tank

[Lance]

Ok, I'm finally ready to hang my new light fixture, but before I actually start drilling holes in my ceiling I have a question for those of you who have run 400W lighting before: How high above the water surface should it be hung? (I'm thinking about 12 inches?) The tank is 72" x 24" deep and 30" wide. (mixed reef) The fixture is a 72" Sfiligoi Infinity XR4. It currently has 3x400W Giesemann 13000K Megachrome MH, and 4x6400K T5's and 4x actinic T5's, and 8x LED moonlights. Wattage will increase from 942 watts currently to 1662 watts with the new fixture so I will start acclimating the corals with a one hour on and one hour off schedule, gradually working up to 8 hours of MH, and 12 hours of T5. Most of the corals can be moved fairly easily and the large GBTA will most likely move on his own if he doesn't like the new lighting. Any advice and suggestions are appreciated.