i love Humidty domes , That and rapid rooters with dutch master's replicator , well i just did my first cuttings and i got 100 % success . You can tell the cuttings love the humidity , and the propagation dome that i got from the hydro store fits tightly and has vents so you can get them air whenever you like . As for the original post , i run my air cooled 600 with the fan right at the end of the reflector , the thing sucks air major ! i got my top canopy at about 6 inches and the girls seem to do just fine , i did the mistake of letting my og get to the glass and she did not like !!! so yea Thats about as close as im going now . it really does make a difference . The 600 will only reach down to a certain point and the more you utilize your spectrum the better .
I am a first timer with about 2 years of literature pushing me to week 6 of my first real flowering phase .