The only problem I see is that Lumenbright reflectors are not good at spreading out the light... they are like car headlamps... a beam/focus of light. I see this as a problem for your tank because it is, well... a frag tank. I dont think you can use lumenbrights and cover a whole 4'x4' area with just two, and the patches that the reflector does cover will be very intense, perhaps too much because its only 10" of depth. So you can raise the reflectors up... alot (like to the ceiling and then some because the lumenbrights still have a narrow focus), but then you get alot more light escaping the sides from the unreflected light the bulbs make.
My biggest suggestion for a 4'x4' tank that is only 10" deep would be to use a single 400 watt bulb in a full size lumenarc... thats if you plan on using a bluer 20/14,000K bulb. If you plan on using a more daylight bulb, a single 250watt 10,000K/14,000K bulb will be fine in a lumenarc. The tank is only 10" deep after all.
Heck, I would suggest T5s over halides even: like two banks of 4x 4' bulbs. That way you can get the bulbs down right over the water and still have a good spread, but you wont lose as much light as a halide mounted up high.
