I have multiple hortilux 1000 double ended hps ru...

Bring them down to 28", then slowly, a couple inches a day, and watch how they respond .. when you get the sweet spot you'll know. Too far and the tops will go into reveg, throw nanners possibly, foxtail, and yellowing or bleaching if too close... A couple inches a day won't cause extreme changes, and give you time to adjust.. keep in mind, in early flower, lights too close can spread the bud spacing, so watch the growth and use the light height as a means of controlling the node spacing..once the flowers are set, and slowed their stretch, then is time to inch it down as far as you can without going past that sweet spot... Cheers!

U should be able to get them within 2 feet as long as u got fans moving adequate air between the lights and your canopy! But remember lowering your lights will reduce their footprints,spread and coverage. But as ur running multiple fixtures that shouldn't be a problem for u. Just ensure to eliminate hot spots from your HIDS and ull be good at 24 inches.