Here's the refined version that will probably be used for the actual fabrication.
Rear-facing area is approximately 3.1 square feet, which is more than the 2.1 square feet of version 2. I estimate the maximum streamline angle to be about 15 degrees, with an average streamline angle of 9 degrees. The center of the cap follows the aerodynamic template.
I'll (probably soon) do the streamline calculations for version 2, and post the results here, too. I suspect they'll confirm the observed streamlines that formed due to driving through the rain.