I think many people has yet to realized some LED manufacturers(not too convenient for me to mention their names) like to use 40 degree lens to pump up the PAR value but at the same time also make the light very spotty fron inch to inch from mid tank up. This in consistency can easily means a thriving SPS and a bleaching SPS sitting just couple inch away from each other at the same height relative the to light source. That's why, if you use one such brand, you should hang them very high. LPS, softies seems not influenced by this factor as much, as I suspect(no science behind this statement at all) they can transfer liquid, energy, nutrients within the puff up tissue quicker and easier.