People seem to have very mixed feelings about pitts mufflers. I have never owned one. I read repots here all the time about low backpressure and not getting enough pressure to the tank. People often have to restrict the outlets to get their engines to run right. If moving the muffler 7/16" will make it clear the fuselage, that is what I would do. Some folks will go to great lengths to hide a muffler. I've never had a scale masterpeice so I am of the opinion that it is OK for model airplanes to have a visible muffler.