Distance above tank for....

[Bumgrundle]

...2x kessil a160we tuna blue lights?
I have a 90g cornerflow Marineland 48x24x18 and am using the Kessil goosenecks. they limit my distance from water to lens to approx 6" unless I purchase the optional 90 degree adapters (@ 20 bucks a pop...shouldn't these be provided with the gooseneck? always been an bone of contention with kessil on this)
Is there an actual "best overall" measurement?

 

[Reefing Madness]

 

[pastelball]

I have a 25 gallon cube with a 160 running on it. I have it 6 1/2" above the water. Running mine at 50% with sps, lps, and softies.

 

[saltyfilmfolks]

Is there an actual "best overall" measurement?

no. IMO the best height is the best coverage. Check coverage first to avoid dark spots in the tank, then check par or lux and make sure you have enough light for the livestock you have.
if you need more intensity and are at 100% , get a narrower lens and move the light higher.