Distance between 600w hps and Canopy?

first grow, got my scrog screen almost filled, just wondering what the 'sweet spot' would be, how much space in between canopy and my 600w hps light. screen is about 4 feet by 4 feet and heat is not an issue as i have a heft fan sucking over the bulb. thanks for any info advice!

close as possible..use back of hand....ran 600 many many grows

what he said, hand test

^^ What they said... but a point of reference.. I have mine 8 inches away... seems to give me the spread I need to fill the 4x4 tent and stays cool... best way I found was lower it a couple of inches, watch... lower more..watch... the plants will tell you when enough is enough...

I run open hood 14"close as I can get.with out bleaching

I agree to a point as well. I have a 600 mh/hps dimmable ballsast combo in 4x4x 5.6h cab...its in an enclosed reflector with 200 cfm fan for exhaust. I have fans circulating air and can keep the light 10 to 12 " away...BUT I find that even tho the plants can take it...at that close a distance....the edges of the cabinet just dont get the same light intensity. Ivve used a cheap light meter and camera light meter to confirm. Sooooo since 600watts covers 4x4 to 5x5 and im on the lower end of that... I raise my lights a few inches higher than the lowest possible point and it really helps raise the light intensity on the edges of the canopy....I can even turn my ballast up a little bit to compensate.
Maybe a better quaility or different shaped reflector would do a better job. ? It helps to use a light meter and actually measure the light intensity in different areas...numbers dont lie.