This is what I imagine is happening to the airflow.
Line #2 goes around the canopy, and draws in line #3 with negative pressure. The lines outside of #3, also get drawn in by the same effect.
Automobile 2 - Odds and Ends pictures by kach22i - Photobucket
The roof wing on my pickup truck works in a similar manner, directing air down, and drawing in the air flow above to make the rear spoiler more effective.
Regarding the Superbird, a friend of mine claims the reason the wing portion is so high, is that it allows the trunk to open. I'm sure the free airflow is important, but the trunk opening is a nice perk, don't cha think?