When I had mine I extended it down to the grate level as well. The idea is it helps even out smoke distribution (and heat) from side to side. If the stack is up high all the heat and smoke exit the firebox, head to the top of the smoker, and out the vent, so your right side is hot and smokey left is cold and very little smoke. The extension forces it to draw from lower down and pulls the smoke and heat back down on the left side before it exits the smoker. Between that and flipping the grill pan in the main chamber upside down you can usually balance out the sides to within 10-15° of each other.