Any restriction in the exhaust outlet tube(s) leads to higher muffler presure going to the fuel tank...and that's usually a good thing for reliable fuel draw....especially critical when using a Pitts style muffler. Pitts mufflers are notorius for reducing exhaust back pressure, and hence requiring a carefull retuning of the carb needles. Some installations simply will not run well with an unmodified Pitts muffler installed in place of the motors original stock muffler. There are threads on RCU citing the virtues of plugging one of the Pitts muffler exhaust tubes so as to re-establish sufficient back pressure and thereby improve fuel flow, thus eliminating fuel starvation problems. I have had to do exactly that on an OS46FX set up, and on an OS61FX too. Further, it would seem to me that a few hundred RPMs up or down, will not significantly, or even noticeably affect flying performance. So, bear this info' in mind as you modify your outlet tubes. There is merit in the old saying..."if it aint broke, dont fix it !". I hope this info' is helpful.
happy flying.