I think it really depends on your rock height. Most I've asked told me 6-10". I think the proper way to do it is get hold of a par meter and test the par on different Heights to find the best height for your tank. Following the brs videos, an average par of 350 is good. If you are interested I have a ecotech rms 17 hanging kit that I bought wrong. Can't send it back cus I've lost the packaging. Brand new and unused if your interested pm me.