not true IMO, anything about a 5ft plant and your not going to be happy with the results using vertical light, unless your able to add overhead lighting to sub the vertical which he is not going to be able to in a tent, knowing your strain and fliping at the right time is going to be clutch, however
the pro sits 12inch off the floor, so that leaves 6ft of vertical growth. just because he is using the pro doesnt mean he needs to use 10k to light it, he has to grow the right sized plant for the space allowed. DHF pulled 9-10packs out of a 10x10x7.5 room for years with a 50/50 sativa/indica
Im assuming he wants low plant count of he wouldnt have bought a 4site UC. a 4tallx5ftwide plant with the right strain can yeild 2lbs, while its not a 10pack I would be very happy with 8lbs off of 3400ws
like I said, I fit 5 huge caseys in a 10x11x7.5, that hit the ceiling, and I yeiled over 1gpw and these plants 4x in size after flip, I just had to tie them back to the cage supports and everything was all good
to work around in there, flip off the lights and it shouldnt be a problem
if you all will remember DD had a log of 9k in a 10x10 room with 4 plants, although he claimed to get 32lbs which is bullshit