So, I've been thinking about a boattail. The issue is the top airflow. The rear of the car has a little notch and lip. You can see it here.
IMG_4459 by
Tyler Linner, on Flickr
The question is: when building a boattail should I treat this area any different than a normal hatchback, or will the beginning of the boattail, coming off the lip, have to respect some aero effects of the lip? I ask this in case the lip acts as a spoiler, and if putting something behind it will somehow disrupt it. I can tuft test this later but thought I'd ask now to have a little thinking/planning time.
(The rear of the car has attached flow all the way until said lip. I plan on extending the sides and bottom as well, perhaps two feet or so, to create an open ended partial boattail.)