I'm guessing that's in centimeters, so two and a half feet by two and a half feet, 5 feet high, your 400w HPS at the top is gonna take at least 6 inches, and your stuff's gotta be around 12-16" under the light, so one and a half feet off the top. if you're in small pots I'll just say they're gonna be 8 inches off the ground. So you got about 3 feet of space to be occupied by plant(s). I think those tents are mostly supposed to be more for veg, you could flower one or two though. Autoflowers might be good, or you could do 12/12 from seed and LST during the first few weeks to try and control the height. I have no experience with autoflowers (though I've heard on this forum that they are less potent) but have a friend who does the 12/12 from seed/clone thing nonstop. He gets about an ounce and a half per plant without lst.