My question - would it make a significant difference to raise the supply and/or return to the top of my ceiling? I have a "hip" roof with knee walls on each side, so the ceiling is about 11 feet high in the middle of the room and slopes down to 4' at the knee walls. I would have to box in the ductwork along the ceiling and it wouldn't be that attractive, so I don't want to do it if it won't help much. If I do, which would give more bang for the buck - raising the supply or raising the return? I could more easily raise the supply using smaller flexible duct than a larger metal return, but if I leave the return as is it will be on the floor of a large walk-in closet. Any thoughts?