Higher certainly helps, but everyone should realize it may not be a cure. With lots of different body types and riding positions, as well as different helmets, the same windshield affects us all differently. In addition, the amount of wind and turbulence you get is also affected by the windshield position (distance from the rider) and the windshield curvature. A slight flip at the top may make a shorter windshield work just as well as a taller, straight one. Differences are subtle; that's why the heat gun "tweaks" Marcel has suggested for some of his shields have helped some of our members. I agree with Bonecrusher that the dealer should have recommended a higher shield...
or that the customer should have done some research. You shouldn't go against the recommendations...you just may not be satisfied even if you follow them.
Height isn't everything, and a shorter rider with a long body could need a taller shield, and there are other factors involved (like handlebar risers.)
-Scotty