I've already stuffed Roxul tight around the liner and the smoke shelf, so when I add my block-off plate, I can either just use a sheet of steel tight to the lintel, or I can add a layer of Roxul (3 inches thick) and have the plate 3 inches closer to the top of the stove with a right angle bend in the front to cover the insulation. Should I bother with the layer of insulation above the plate since I already have the smoke shelf stuffed?