The clay was formed to follow the lines of the car and the only areas that aero would have been affected was at the leading edge of the car where the clay rose about an inch above the sheetmetal and wasn't tapered much, then when the clay was removed, they stuck it in bins and threw those in the back seat of the car. They also set the test up so that it was only at highway speeds, no stop and go. If there had been some stop and go involved, it should have hurt the average. Kinda hurt watching that car hit bumps and rises in the road, you could see the car hitting the bumpstops hard enough to get the sidewalls of the tires to flex
I'm feeling a bit ornery today, think we should all write in and suggest having a vinyl top put on hte car to see how that affects the cars mileage too