Nature hates 'angles.' HONDA probably has already incorporated some plan-view body camber at the CR-Z's rear. Once you've got enough clearance for the rear skirts down low, at that point you can begin a 'lead-in' transition into your boat-tail plan taper.
If you just abruptly introduce an 'angle', you've thrown in what will be the adverse pressure gradient which will trigger flow separation right there, violating what Dr. Hucho tells us IS the real solution for 'aerodynamics.'
If you can locate the 'top-view' photographs of Daimler's, M-B 1978 C-111 III, 2016 M-B IAA, and 2022 M-B EQXX, you'll see how they handle the boat-tailing transitions.
