I was actually trying to make good use of my time--sleeping!
However, I jumped out of bed at this idea.
For a given body moving through air, does the air itself care the size of the body?
Let's say that we could purchase plastic or fiberglass boat hulls that fit the template perfectly for a Prius. They might be too narrow or wide, but couldn't you cut it down the middle and trim or add spacers?
Now, if that is the ideal taper, what about objects of other sizes? What if you had a big and rounded old bus. I doubt that the corners would fit, but let's say that they do. The shell is too wide, so you cut it down the middle, cut a piece of fiberglass of the correct curve, and attach it. Would you continue at 22°?
If I boat-tailed a go-kart (I bet that you won't dare me to!), would I have the full 0°-22° taper (could I still use part of the theoretical boat tail?) or, since it would be so much shorter (vertically), might I only get to 8°?