I had a 13 and dropped to the 11. I am 5'10". The Madstad works so well I have considered going shorter. I ride 40+k per year and this windshield works as advertised.
Curious why you dropped to the 11" ? Was the 13" too high in it's lowest position? I'm same height as you with a 32" inseam and I ride with the 13" but have been considering the 11" also.