I think George was talking about my lift from the sides idea.
As far as the taper goes, we gotta keep in mind that attached flow is not the end game, it is merely something that needs to be present in order for something to be aero optimized to minimize drag. It's like saying if you have Air you'll have a fire, well, no, you need wood and an ignition source too for a fire. With low drag, you need attached flow that is not creating havoc with vortex generation. I'm still pretty convinced that flow remains "Attached" at sub template shapes but in doing so often creates more drag by generating large vortices.
However, by keeping your cap high enough and very close to the template, I think you'll avoid a large low pressure area on top and will therefore not be trying to pull air up from the sides. Ideally, all the air just flows straight back. I think you'll get some air spilling up, but no enough to have a gruesome effect, and you're wanting the room inside anyway. Had you try to drop it to the tailgate top, I think you'd have needed the sides tapered. The Prius is definitely sub template with very little taper and some very square corners. You have great radiuses and are closer to ideal shape. A8ksh4 plus 2!
In short, fret no more, you're safe. Great Awesome JOB!!
