the burnt tips might be your Nutes too strong, or not ph'ed. You have to ph every feeding, but I'm sure you know that. I have (2) 400 watt LED, I have them at 12 -15" and on the side I have T5 bloom spectrum and I feel you get a nice light spread. without the power of HPS. Which I have and don't use..

Also, don't hang them just strait down, use angles, make the light cross paths, compounding strength, on a small garden.