Enlarging PRP doesn't always help

PRH said

Conversely, I have also see it where the SSR is working well, and the flow numbers are good, and the drop off at high flow is minimal.
Then you go in and open the pinch up “more”, and all of a sudden the peak flow is less, and the upper end of the curve falls of worse.
My take on that is the SSR can no longer manage the volume of air trying to get around the turn, even if it’s only in specific areas of the turn.

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This is what I believe as well. Erland Cox has a good thread on Speed-talk about chamber stall. His theory is that the wake from the flow separation on the short side continues to get larger and shuts down the flow area. The 'wake' is actually the boundary layer growing larger and getting forced back up the port by the high pressure in the combustion chamber. I have verified the flow reversion and swirling with my testing with the pitot in the chamber.