Bought a new stove, removed existing microwave hood and the cabinet above it. The existing duct work is oval, opening is 6" wide by 3.5". My new hood requires 6" round. I went to local hardware store, bought a 6" oval to 6" round universal boot- doesn't fit. The oval opening on this boot is actually 7-8" wide opening. Not sure why they call it a 6", but it's wider. Looking for easy fix to use existing ductwork. I live in a town home, duct is running thru shared party wall. Im limited to what I can do without cutting into walls/ ceiling.