im thinking of replacing my 4 powerheads (4ft tank X2X2, 120 gal) with a 6100 + 7091. the way the tank is set up is 2 rockpiles with an open bit in the middle and the front open also. I was hoping to have the 6100 in the middle on the 2 rockpiles facing the glass (which is only 2ft away) and hitting that then using that to throw the curent back onto the rocks, will that be ok... i know most people seem to have one each en, or just one at one end...