How many GHL mitras for my cube?

[lastlight]

i currently use one on the exact same tank and i'm happy with the coverage. it's def shadier near the top of the tank at the back but i'm fine with that. in the future i may add another when the tank is filled in as it might be needed to avoid excessive over-shading.

i'm currently ramped up to 61% output and have the light about 4 inches off the surface. i'd get much better spread lifting it higher but can't due to the glare from the unit.