The recommendations on their site for shield sizes are pretty spot on in my opionion.

I'm 6'1", but am long in torso. The site recommends a 15" shield for me, and that is what I ordered. I look over the shield regardless of its position (high or low). With it high, it's great for highway speeds or windy days and it creates a very still pocket behind it. In the lowest setting, it's great for non-highway speeds, and I get a nice little breeze. Since I like the ability to go back and forth within a ride, I created an electric linear actuator system to move adjust it while under way.

By the way, for me, this unit replaced a Clearview Full Wing +4 wide with vent (i.e. the shield was 4 inches taller than a full wing shield, and was wider at the shoulders). The AngryStad is quieter and smoother by far.