[COcyclist]

Daq, If I understand it correctly, the "phantom body" would be similar to the idea of pick-ups having less drag with the tailgate up. It's not as perfect as an aerocap or full boattail but you still get some of the benefit. With the tailgate up, you have a captured bubble of air that the slipstream slides over. You may not see much difference tuft testing on the rear glass with a trunk extension because of that captured bubble above the trunk but you may have less drag. My suggestion refers to a couple of vertical extensions inside the tail lights at the outside edges of the trunk. The rear end of the extension would match the 7º(?) plan taper from the sides of the car and help blend the side airflow in addition to the airflow coming over the roof and the trunk.

You have me excited to try this concept on my hatchback. I have started on a cargo box style form that would attach to my receiver hitch to serve as a "phantom boattail". Hopefully, Aerohead will weigh in if I have this all wrong.