I put my lights up as high as they will go in my tent and turn them on the brightest they will go... I figure seedlings have to deal with the sun in an outdoor grow and they do just fine - so this has been my approach from my first grow until now... and I've had no regrets... If you find your seedlings are getting leggy with too much stretch, just lower the lights to about 24" - but I've never had to do that. It will all depend on the lights you have... if they're weak, they'll need to be closer.
Good luck!