This is no voodoo. Just stop for a minute and think about how many thousandths of an inch difference a Bach 1C, 1 1/4C and 1 1/2C rim and cup have. Think about the microscopic difference between a ML and a large bore horn bore size. Think about the miniscule difference a valve alignment represents. What about the small differences in your tuning slide to get "comfortable? All of these things are in the same geometrical ball park as aligning the mouthpiece in the receiver. Before doing this, make sure that the receiver and shank are really clean. Dirt and other crud can affect the mechanical coupling. Optimally, the shank should be lapped into the receiver until the gap is right. The beauty of this tweak is that it is FREE, does not waste practice time and is repeatable. keep in mind that if you remove the mouthpiece from the horn when it goes into the case, the shank will wear and you may need to recalibrate after a year or two. My take on this tweak is that it is not airflow, rather the mechanical coupling of the mouthpiece to the horn. Any slight out of roundness will dramatically reduce the coupling. There will be a sweet spot and when you find it, the horn should react more consistently, stable, focussed.... Thanks Wayne!