My experience matches John's. I change the height depending on temperature and wind conditions. When it's hot , I've taken the top off to get straight wind at shoulder height. I keep a helmet bag under the seat to store it in.I'm 6' and have the airflow. Can't comment on the non-adjustable, but the airflow completely changed the ride characteristics of the bike for the better. Along with much less wind noise, the stability of the bike is much better.
I have the top part about 1.75 in. Below the top setting.
Hope that helps.