Thank you! I am so sick of hearing people talk about the inverse square law, it doesn't work that way with multiple light sources and/or walls. If you are talking about 1 light source and no walls nearby than by all means talk all you want about the inverse square law..
It still applies to multiple light sources. Even though those light sources overlap each other, each point of light is still spreading at 120 degrees (or whatever the lens angle is), meaning the higher you raise the lights, the more of that light hits the sides of the grow room/tent and is reflected - assuming you have reflective sides, in which case it's lost if you don't. In any case, reflective material may only be 70-80% efficient, and there are atmospheric considerations also (minor, but still applicable). So any way you cut it, you will lose some light intensity as you raise the lights.
The REAL trick is to find the distance that gives the most even light coverage while maintaining light levels within the 500 to 1000 Umoles range.
I agree you want to aim for even coverage - however you define it - but not everyone has par meters and of course different strains can handle different light levels, so even though the numbers might be a good guide, IMO you still have to read the plant to see what works best.
In practical terms, there's probably a point where you get even coverage and where you can adjust your light intensity to suit the individual plants. From what I'm starting to see with strip LEDS, good yields can still be had by spreading the same amount of light over a wider area, but you end up with more popcorn and fewer nuggets, so it becomes a compromise between overall yield and how much you want to trim!