That's a great looking room!
I think you are probably right about that earlier ceiling bounce on the left having a noticeable effect. Fiberglass as noromance suggested is more effective. 2" thick Owens Corning 703 should be enough to test it out. It might work best to treat both the duct reflection point and the right side ceiling as well to keep it symmetrical.
I think you are probably right about that earlier ceiling bounce on the left having a noticeable effect. Fiberglass as noromance suggested is more effective. 2" thick Owens Corning 703 should be enough to test it out. It might work best to treat both the duct reflection point and the right side ceiling as well to keep it symmetrical.