Thanks for the replies everybody - there's some good thinking going on out there.
Having thought about it a bit more, there's one thing that occurs to me although it could be considered a bit of a cop-out:
I know from my own calcs that the best you can do in engineering mathematics is an accurate approximation - we do qualification/certification testing in order to prove that our theory is correct.
Having done the flight testing at the designed cruise speed; is it perhaps considered too expensive/time consuming to correct a "minor" innacuracy in incidence setting and still meet delivery requirements?
However, I'm not giving up yet!