scottoriou,
That's definitely a nice trend.
California98Civic,
I have this idea that the airflow won't follow a curve without having a physical shape there for it to follow. I'm guessing there's a separation point as it tries to follow the downward curve of roof + rear glass. After separating, I think it would continue in a straight path if not otherwise influenced.
So for the airflow after the roof, I drew a blue line tangental to the final roof curve, starting just before the rear glass. Then a 2nd blue line which would be a spoiler that meets that line.
Both the earlier red and black lines come close to the blue line I added. The red line meets my blue one just about perfectly; the newer black line extends through it just a bit.
What do you folks think?