As far as spacing between light 1 and light 2, i dont have experience with HPS, but ive read you want a decent ammount of overlap between the lumenous "footprints" of each light on the canopy. Sorry i can't give you more, better knowledge. Hope it helps a little though.
air cooled ? is there a fan blowing over the plants ? open hoods ? bare bulbs ? usually put 600 watt hps about 1 foot away here non air cooled but in a reflector .
Grab yourself one of these and m ake sure you dont have any hotspots. Noone can give you an exact height for the setup you have, since every setup is different. Grab one of these for 13 bucks or cheaper somewhere used and move the lights till you have it perfect and no hot spots and your good. Good luck