With the pitot reference giving such stable readings, I was able to do a test on the Insight that with the previous sealed reservoir approach, was difficult/impossible. I used a 0-120 Pa Magnehelic gauge (ie 0-0.5 inches of water FSD - so very sensitive).
I placed the measuring puck on the bumper corner and recorded a two-way average of -30 Pa at 80 km/h.
I then added a large separation edge (always go large when testing - if it works, you can always go smaller.) Note that the measuring puck was not moved.
The pressure increased to -17 Pa (similar to the pressure previously recorded in the middle of the wake).
So the separation edge measurably and clearly reduced the vertical suction peak down the side of the bumper.