[aerohead]

*I'd want to analyze the roofline for deceleration overshoot. NISSAN has used a CALTY roof like that on their Z-Cars for decades, but they never demonstrated any remarkable low drag attributes. It might be okay, but it would be prudent to validate.
* On the rear diffuser, I'd take the SAE 10-degree 'departure' angle, projected up from the back of the rear tire/ground interface, and lower the rear transom lower trailing edge to that imaginary line. It's my opinion that, the up-slope as presented, would never support low drag.