I would say it will easily do 30 inches and the depth is probably 30 or so too. The light has a ton of power. It really depends on how high you hang it.
It would be about 4-6" above the water. Tank is 27" deep. 36"x36". Currently I have 2 black boxes and a 4bulb T5. Was thinking of moving the t5 to my frag tank and putting this in between the black boxes