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Really -- I would have thought that smaller has lower Cd and lower area, too? A larger car has a larger wake which mean higher drag, all else being equal.
Since the Cd is already under 0.3, that means the area would have to be reduced 3X more than if you reduce the Cd.
Let's say a typical car has 30 square feet of frontal area and it has a Cd of 0.33, so CdA is 9.9sq ft.
If you reduce the Cd down to 0.30 that reduces the CdA to 9.0sq ft. To match that by reducing the frontal area, you have to take away 2.5sq ft for a total of 27.5sq ft.
If you reduce the Cd down to 0.27 that makes the CdA 8.1sq ft, and to match that you'd have to reduce the frontal area down to 24.5sq ft -- that means truncating about 1 foot off the height, which greatly reduces the interior volume of the car.
So you get a much smaller car. Reducing the Cd can be done without compromising the interior volume.
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