This is the technique. I've used it, many others have. Allow your hand to feel the warmth for a short time, determine your height you want the plants to feel that warmth because they're the ones baking under this light for nearly 24/7.What's the right point? As close as possible. Once the light has fired it will take 5 minutes to get up to full light strength, wait 30 minutes and you'll have a good sense of the heat it throws. Put your hand (palm down) under the light and feel how hot it is at different distances from the light. This is the same heat your plants will feel, so if you hand says too hot your plants will react accordingly.
I'm fortunate to have enough special area above my lamps for heat dissipation. I do not have the ventilation ducts on my fans, but I can see them being very useful had I really needed them.cell: Hood design plays a big part in that. I keep my 400hps 12inches away from all strains except some heavy sativas that foxtail with the light close. My hood has removable flanges for air cooling and I have 4" flexible ducting running to a 4"-> 6" adapter then to a 6" inline duct fan. That reflector was part of the package. Ducting, adapter, and fan fan sold separately. ;)