12 deep? i don't think you need a 400 watt halide. i'm not understanding what you are asking though. try using punctuation and typing full sentences.
i'm guessing you have 2 x 250 watt halides over a 6' tank. the general rule for halides in spider reflectors or similar is 1 lamp for every 2 feet of tank.
you would need 3 lamps total for this system.
i would think a 400 watt halide would burn corals under 12" of water
You need three reflectors. Lumnebrights will give you incredible par. Lumenarcs are good too and will be plenty of par for a tank that shallow. Don't use 400 watt on a tank that shallow. It is a waste of money and may fry your coral.
For a 6' tank mh's are much more economical and easier than t5's. Like everyone has suggested your going to have to bite the bullet and get another mh on there. Or you could use the light mover with a 250w mh.