Not true. I have a 600w HPS and my plant is 14 inches away. I raise it to 18 inches every week or so. Also, my temps are only 81F. I do have a air cooled hood though with a 25 foot duct running to my ac. If I got a proper exhaust fan I would have lower temps. If I were you, switch to a 600w HPS. I’m day 42 today from sprout. You should have no issues with lighting for veg of flower for your 4x4. If you can’t get a 600w hood, just use the 400w HPS with no led and keep it about 14 inches from your canopy