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In fact, I have often thought this would be a very valid criticism of my pressure measuring techniques with the puck: How thick is the boundary layer where you are measuring, and does the puck disturb that?
And the answer is: I just don't know.
Of course, flush holes in the car's body surface would be best, but that's a bit hard in your daily driver.
When developing the measuring puck, I went through a whole bunch of techniques, with Dick Barnard commenting, and this was the best I could come up with. (I'd not seen the Scanivalve one at that time.)
And, when my on-road measurements matched Jaguar's CFD, I became pretty confident.
And Cr45's suggestion (here) of using the pitot static port as the pressure reference (instead of a sealed vessel) was revolutionary. (I have, via PM, asked him for his real name so I can publicly thank him in my books and Youtube videos, but he is shy.) His suggestion took my pressure measurements to another level - indeed, a radical improvement, and a major reason for my doing the update book.
So I am now pretty confident that these aero pressure measurements reflect reality, but with the caveat that the further you are towards the front of the car (and so the thinner the boundary layer), the less valid may be the pressures.
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