Quote:
9.1.2.F.14.C (p323):
"The entire wing assembly shall be mounted 6.0 inches below the highest point of the roof or roll cage main hoop whichever is higher measured at the highest point."
9.1.2.F.14.E (p323):
Cars with a wagonback/notchback/hatchback style body must have the entire wing positioned between 6.0 and 28.0 inches of the rearmost bodywork as measured along the vehicle longitudinal centerline, and a maximum of 4.0 inches above the highest point of the roof. For this subsection, a wagonback/notchback/hatchback style body (or variations of these) is a car in which the rear edge of the roofline is no more than 28.0 inches forward of the rearmost bodywork as measured along the vehicle longitudinal centerline.
I've been told that the source for the 28" is that members of the GTAC "went around for weeks measuring dozens of cars. When they put it all together, 28 worked."