Every since I made the posts about hanging the light fixture high (120mm) to fit the fans, people have replied I hang the light too high. Every since I tested the light with a light meter and lowered the light (3.5"), other people have replied I hang the light too low. lol.
Apparently, different people have different idea on what's the optimal height.
Anyway, my take is that it depends on the reflector on the light fixture. Some light fixture like mine is at it's optimal to have it hang about 3.5" above the tank edge for the middle of the tank. An inch or two higher would lost 25-50% of the light. That was tested and measured in my tank with a light meter.
The bigger light fixture that have a long focal length reflector, you can certainly hang it higher.
Sorry, I think I only confused you more. lol