wait till u switch to a 1000w HPS, much hotter, this is the reason 600w's are similar price , less heat plus better lighting spread if you use 2 spaced apart, i have a 1000w in a 3x6 and it doesnt get good performance at the 5-6 foot , another thing is i have an air cooled hood 450cfm fan on it and it keep the room in the low 80's, with that said i can bring the light down to about 6-8inches, this always give me light bleaching....i have a few 1k's and so far it was not a good investment, whats the point of having an air cooled hood if i cant put the lamp inches away right>? my HPS gives off 150,000 lumens in an 18 sqft space, they say 6500 lumens per sqft is ideal, im around 9200 and its a waste of lumens on the plants directly underneath...so the moral of the story is even if you had an a/c to control temps or air cooled hood you will get bleached plants if our not carfeful, every 12inches in distance cuts the lumens in half////i believe the distance your looking for is 16-20 inches, just hope the heat is ok....good think your running MH , they are so much cooler burning