[alanmcorcoran]

Some of it is going to depend on the windshield. Briefly:

1) Unless you have a really huge windshield, you are going to get some wind.
2) It shouldn't hit you directly in the face though. (mine tends to buffet a bit above and behind the helmet.)
3) there's three main things to look at: too high (wind coming underneath, hitting hands or chest), too low, (wind hitting your face) bad "rake" (angle is too severe or not severe enough).
4) one last thing is some can be mounted further "out front" or closer in. Hard to say which is better - I think the big ones can go out front more and the smaller sometimes do better closer in.

The best thing to do is to note where the wind is hitting you and where it is coming from, and see if you can move the windshield so that gap is lessened. (I know, "Thank you, Doctor Obvious!") Trust me, I have screwed with mine plenty and I could still go a few more rounds with it if I was riding it more often.