Light mover and distance from canopy.

I currently have a 600 watt aircooled HPS on a 5 foot light rail. I currently run the light about 2 inches away from the canopy with no problems however I am wondering If I should move the light further back for more coverage as it stands right now when the light moves all the way down to one end. The farthest plant barely gets any light. Granted it moves back rather quickly but I am still wondering whats better.

Should I bump the light up till its covering the entire area on each pass through or is the intense close light better?

I would move it at least 6" off of the tops a 600 should have deep penetration.