If you'll go down the home page here at the Aero Forum to the Tread: new mercedes b class 0.24 Cd ,go to page-3,#34(permalink) and click on "Aerodynamik Report" you'll see a 3-D flow image of the VW 1-Liter Car.
If you'll do a Template comparison you will see a very close match and where the VW goes hypo-Template you'll see a corresponding thinning of the smoke as the boundary layer is being compromised.
If you do a 3.92:1 section on Flow-Illustrator you should see something similar.
Or put just the upper half of your image in there and see what that does.
