Have you considered a adding a splitter at the lower leading edge?
I know people think it's just for adding downforce, but I think it's works to keep air from going under the car too.
Project Import – S2000 Front Wind Splitter “Backyard Aero”
Nice detail photos you have provided - cool.
http://www.electricmgmidget.com/inde...ing-an-air-dam
