I was contemplating a box cavity taking up the entire hatch area, allowing a section to extend off the rear roof at least 10 inches or so. Then I got to thinking about how much those curved corners must contribute. Thanks for pointing that out guys. I mean here's the evolution of the same type of design (essentially the 'new version' of the same body style), and it's .295 cD! Note the smaller mirrors, and the side profile is slightly different.
Just based on putting this information together, so far
I think some small restyling tests on the rear of a 3/5 door 00-07 Focus could make a very large change in the cD. I think this warrants far more attention on testing vs the tire spats or front under panels I've made.