isn't there something like the inverse square law of radiation MacG liked to talk about, every inch light travels away from the bulb the growing properties of the light diminish.
I dunno if this helps
"In general minimum amount of lighting needed is around 2000 lumens per square foot.
Optimal is around 5000 lumens to 7000-10,000 or maybe even more, lumens per square foot.
No matter the type of light, if you can find the exact specs for its lumens/FLUX per square foot (or the equivalent PAR for red/blue only LEDs) you can use this as a loose guide as to what you need as minimums:
Seedlings and clones require about 400-1000 lumens per square foot.
Vegetative growth requires about a minimum of 2,000 to 3,000 lumens per square foot.
Flowering requires about 5,000 to 10,000 lumens per square foot, ideally, and can take possibly much more.
10,000 lumens is supposed to be about the average power of the sun at sea level on a clear day at high noon, or something like that, lol.
8,000 - 12,000 lumens is supposed to be about the power of the full sun without any overcast or no clouds.
It’s not ideal, but you can make do with 2,000 lumens for an entire grow if necessary."