Welcome to the age old story...
ST1100 Standard screen = Buffeting wind into helmet
You can do a number of things:
Fit a taller screen (can help, but can block out to much wind, and take a lot of the feel out of riding)
Fit a smaller screen ( opens you up to the world more, terryDJ rides his 1100 with almost no screen at all)
For an Australian supplier:
http://www.eaglescreens.com.au/wp-content/uploads/2011/09/H-71H72.docFit a Laminar Lip,
The Laminar LIP is designed to quiet wind buffeting and reduce wind pressure while raising the wind comfort envelope, this link takes you to who sells them:
http://www.laminarlip.com/st1100.php (they also sell screens as well)
The lip is what I am going to try next, i have heard favorable reports of it taking away the crappy air and smoothing the ride out, although it does not look as pretty...