A change in diameter, restriction, baffle, or anything other change in the exhaust path that causes a pressure change (reflected wave) may "cancel" an unfortunate (and accidental) flat spot, hesitation, etc. in even a docile engine.
In some cases the factory exhaust system has been designed to eliminate such a hiccup.
This always reduces exhaust gas volume at peak power, although there may be a small improvement (partial or complete cure of the flat spot) in torque especially at part throttle and mid RPM.
Anticipating a problem and adding a restriction where it was not needed may appear harmless, since the only effective test is... to remove the restriction.
An easy, cheap, and reversible test is to add a short section to the final tailpipe at least 1/4" smaller ID. Your FLAPS has these as adapters. If this size change is not available, simply crush one end into a "stadium" shape. The circumference will not change but the X-area will shrink.
