Man oh man, what strain of Tomatoe are you growing/ I've heard of grafting the Hops plant on to the root system of a Marijuana plant, producing a vine that looks like Hops and the genetics of Marijuana actually growing. Doesn't work at all. So I'd be interested in a Tomatoe version. Great stealth grow; could plant out behind the police station...Best test of "How high above the tops should my 600W light bulb be at" would be to hold your hand there and wait a few minutes to feel the heat. If your hand can tolerate , it is fine; if you feel too much, raise the fixture. I have 600W HPS on light movers so I can actually go lower than a stationary reflector and I am at last 18" above, so I'd venture to say that you are too low.