Until there is a shit-ton of foliage to absorb the light, and given that all of the surfaces we can see in there except the smartpots are reflective, you have to keep the lamps that high to not overlight the specimens.
Because you can't run all the lamps at once when they are that size, you will piss them off. So you have to run only some lamps. And if the lamps were too low, it would serve to illuminate the room far less evenly. Part of the strategy of keeping the lamps that high is to even out the illumination in the room. That is what my experience with vert taught me, anyways.
I saw a pic in a thread on this site a year or two ago about lamps. It showed how irradiance off of a 1k hps was at maximum at a 90 degree angle to the arc tube(perpendicular) , dropping down to right around 50%, maybe just under 50%, at a 45 degree angle to the arc tube.
Until the plants have enough foliage to absorb light, and eat high enough ppms to process that much light, it is counterproductive to add too much light too early. They will get pissed and stall, and it takes up time getting them to recover.
I went to overhead lighting and scrogs, I feel that I can get more production per ft2 out of my room that way vs vert, as I am limited on space. But veg time is longer than in vert like this. I wonder sometimes if underlighting large enough scrogged specimens would be worth it, get 2 planes of growth, more results/ft2 maybe that way. Trying to keep up with the big vert kids with their 4 planes of growth due to the 4 sources of light.
Mr. Goodcat, your work makes me think of going back to vert sometimes. Thanks for putting up your thread so we can learn from it. Some cool cool shit.