I have an older Vermont Castings "Defiant" it has an ovalized 8" outlet. I want to put a SS sleeve in the approx 7X11 flue. I would like to use 6" round and adapt down from 8 to 6 prior to connecting to the liner tee. I don't want to use the 8" ovalized as I will be replacing the stove someday and assume that most newer stoves are 6". Do I face any issues choking down the stove from 8 to 6? I have heard that the stove was made in 8" to allow operation with the doors open using a screen, so maybe 6" won't be an issue?