What kind of corals do you have? for a mixed reef with sps in the middle 24" x 40", you could use 1 32" controllable fixture with 120 degree optics. You would have some shadows that way, if you want complete coverage, I would reccomend 2 value fixtures with 120 degree optics with the long way front to back, or 2 24" controllable fixtures with 90 degree optics, oriented the same way the value fixtures would be.