I've never tuft tested the parts of my boattail that I can't see from my rear window since I don't have anybody here who would be interested in following me to watch the tuft behavior. Also, unless you were driving a very low slung car, it would be hard to get a good view of the underside of the boattail from behind (and I don't have a video camera to play with). But the rear sections of vehicles that don't have attached flow tend to collect dirt from the turbulent air flow and the underside of my boattail remains mostly clean, so its airflow looks to be mostly attached..
Here is the Google Earth image of the Aerocivic.
