I have had this same annoying problem. I found that the adjustment for the windscreen simply does not allow full adjustment. I took out the bottom screw and nut and was able to adjust the shield a little more straight up and down and it nearly cut all the buffetting out. I realized the solution when I had my bike in the shop for maintenance and the owner let me use his Road King and I noticed his screen was MUCH more verticle. Unfortunately it appears to be a design flaw and would require some machining, ie lengthen the adjustment slots, to make it permanant.