You need more/stronger light IMHO, and Id have the one you have down closer. I run a 635w Gavita 1700e at no more than 24 inches. I also run a 1000w HID at 24 inches, or closer. Depends if I can keep the temps at 84f or less for the HID.... In the mid fall- mid spring no problem. I also have really good air flow.
Think about how bright the sun is at the equator, at noon, on a clear day, at 3000ft-9000ft and contemplate your light.
What Diodes. Watts dont tell the whole story. But you need way more light. That light, especially at that distance is like trying to grow weed at Dusk.