In my case the head shaking problem was definitely coming off the top not the bottom. The rubber strip made it worse, it may have deflected the stream a bit, but what hit my head was more buffeted. I couldn't read a sign over 60. While riding, I can put my left hand right at the top of the screen and feel the increased stream of air coming right toward my face. If this is the case with yours, lowers are not going to help. Only a taller screen will move the increased airflow over your head.
