I'm playing around with different configs/footprints, that tent you're referring to is actually a different grow. The LEC runs are in my main flower room that's 4x9.5x7'. I ran 2 plants initially as I pulled 3 males out of 5 plants first round I got it. I ran 4x plants in 5Gal after that run, just finished it about 3 weeks ago and pulled 10.9 zips from that one. Then I ran a large Blue Dream by itself in a 7Gal pot that took up about 24" x 36", it was just a test to see what I could pull from a larger 7Gal plant, that came in at 7 zips dry. Right now I'm running 2x 315w LEC's side by side in a 3x6. First 3x3 I'm running 6x plants in 3Gal pots, 2nd 3x3 I put in a week ago, that's 3x 5gal and 2x 2gal smaller spare clones I had.
It depends on size of the plants and typically the pots they're in. The 6x 3Gal plants in the first 3x3 (were put into flowering at about 16-18" tall and they're now about 24" tall) and filling the 3x3 after stretch. The second 3x3 in 5Gal's were about 24" tall going into flowering, they'll end up around 30" tall, then I added 2 smaller plants in 2Gal to fill in the open spot, they're now filling in the 3x3, when they finish stretch next week they'll fill the full 3x3. You have to guesstimate the final size by allowing for stretch depending on what strains you're running and how you've trained them. If you have the veg room or flowering them in the same space 4x 5Gal or 6x 3Gal will typically fill a 3x3 well.
The thread I've been posting those runs is the red link in my sig if you want to read through more details. I tried to upload a shot of the current 3x6 (2x 3x3's) but there's an issue right now trying to upload files, will try an update it in my thread once whatever's going on right now gets fixed. Cheers.