I could write great lengths about this, but I'll try and keep it short.

My short friend tried my bike with the original screen and said he got headaches from the turbulence. I didn't notice myself.
Later I put on a taller screen and lived with the turbulence for the longest time, but only at higher speeds. Believe it or not it's just recently that I put back the original screen and thought hohey! turbulence is gone!

So, with the original screen your head is probably right where the wind travels over your screen. Like mine was with the taller screen since I am quite tall (2 meters). I read all about putting bird comb where the forks are, making plastic plates to cover it or putting on huge tank bags to stop wind coming up the forks. In the end it turned out to be as simple as putting on the original screen so the wind hits my chest/neck instead of my helmet. I also read someone chopped the original screen to make the same effect. May be worth a try? Just take it off completely and go for a test run first, only be aware of the difference between normal wind and actual turbulence that shakes your head so much that it almost blurs your vision.