I ran one set of manometer tests up the centerline from lower IC lip over grill, nose, cowl, windshield, roof to end of out "wing" Pressures were below atmosphere in center of roof, typical, but I was surprised to find higher than atmosphere at the top rear of wing. So it is adding a little downforce as is. Be fun to measure the effect of the wickerbill.
I have heard folks say that closing the openings would make it work better, but from my aero testing, Ford did not leave much on the table. I did not do comprehensive testing of the wing, but since it would be cheaper to have made it without openings, I bet they do something useful.