I think you should raise the lights also but 8" -12"is not necessary. 8"-12" sounds more like a preference. I would raise them up enough to blend the dark middle area in better, that could be 2"-20". The most important factor in lighting height would be par. What corals are you going to keep? What par do the corals need etc... but since you are new I would lean towards having the lights aesthetically pleasing through out the tank and when/if you venture into corals that need more par then you can borrow a par meter which would give you a better idea of your specific lights output at differect height levels.