That is about the max area I found the H80 to be effective. It covers a large area but not with enough intensity to be effective. The biggest issue I ran into with the H80 was it's ability to penetrate more than a few inches. The H160 improved that a little bit (I have both running over our refugium at the moment to see if I can lower nutrients further than the H160 alone but dont have an conclusive results yet. I heavily feed our fish so I'm asking more of the refugium than most reefers.It's part of my sump. Water volume = 12w x 12d x 10h.
But I'm sure it would be effective on a fuge twice that size as you could adjust the spread by raising or lowering the light.