Had a 20" Madstad on my previous GT and had one issue with it. At it lowest setting, in really hot weather, it was too good. At it's lowest setting I wanted more air. Ideal height , for me, would be airflow that just hits my helmet vent. Considering an 18" this time but don't want to lose the still pocket of air that I had with the 20" in "normal" weather. I want a blast of air in the lowest setting and still air in the highest. Anyone have any experience with an 18" Madstad?