Chaz, some food for thought. Your simulations are 2D. The Beetle is 3D. Air coming around both sides plays a major role. When air is displaced it compresses. Once the object passes it can expand. It cannot expand immediately so a sphere or cylinder draws a wake. In 3D the longer the roof (think limousine) the more time for top and sides to equalize with each and blend with surroundings. So, less stored energy to be recaptured by the tail. Thinking about the physics and math, it stands to reason that the ideal shape might be related to a sinewave or gaussian bell curve. Those are two of nature's best shapes. Take fish for example.
One more thing. It's possible this guy know something we don't.
Cheers
KB