Well, moving the power heads down wouldn't be just for the coral, rather you want to stir your tank... and right now your just stirring the top water... you want them to push the excess waste/nutrients from the bottom/falling, up to your overflow so that they can be filtered out... if your power heads are too high you may experience a build up of excess food/detritus collections on the bottom of the tank...
Also I didnt realize you had intention of adding coral, I thought it was a FO tank... in that case I would strongly suggest sealing that display piece 100% before adding any coral and also consider using more LR, not only for adding more space to place corals but also this would be a situation where LR starts to become more beneficial at filtering than a Wet/dry using bioballs(IMO)...
Not saying to make a refugium or anything of the sort to start with but I would suggest running that tank as a FO(fish only) for aslong as you can, to get your feet "wet" in the marine world and to allow yourself time read up/research on keeping a reef and making things like a refugium,deep sand bed etc...
If you have any question, feel free to ask, we have tons of very knowledgable people who love to help.