[kach22i]

Whether you utilize a pressure relief method (diffuser) or attached flow method (2.8 degree plane) for ejecting the air moving under the car, I think after seeing the belly of a stock Prius you need to incorporate a full belly pan to any design you are considering.

Just in case I wasn't clear before.

Anything you can do to limit the mass and surface area of your "bustle" is a good thing in my opinion. Weight and handling will be affected by the mass. And cross winds pushing on your stern will be affected by the surface area.

The initial want or inspiration of doing something big and simple is not lost on me, however if your are up to the challenge of doing something craftier there may be benefits to it.

I do see a transformation in thinking taking place as the thread progresses, and that is a good thing in my opinion. Exploring all your options is the fun part, the hard work is in getting it built and suffering the disappointment and heartache of the setbacks to come. Overcoming these as now unforeseen setbacks is the ultimate test and the ultimate reward.