Actually, my tank bag seemed to eliminate the head buffeting . . . Plus, I cut the hump out of my seat so I could scoot back further on the seat.
The main difference is reducing the air coming around the stock windshield. I sit pretty high in my seat (where the hump was, which is thicker) . . . You may need to shorten your windshield if you are getting head buffeting. Or, try moving your tank bag forward or back.