I attended briefly this weekend the Carlisle Lakeland Winterfest car show, and they had a display of some past year SCCA racing Vettes with wings, obviously there is an evolving understanding of the issue in question. They seemed to, with straight wings of the era, be referenced off the most rearward single rear point of the car, rather then any outline restrictions.

Reality check, that half the population is smarter then 50% of the people and it's a constantly contested fact.