99, you are not alone my friend.
I have the same windscreen. I use it when I ride down the pavement roads and in winter (some). I noticed the same issue as you, particularly the height issue with buffeting wind in my face.
I will some photo's of my solution so you can see what I did, but will explain it here so you can see where I am going. There is more than one way to [s]skin a cat[/s] mow a yard, but this is the approach I used.
I found a tinted car plastic sun visor extension. Sun visor is thinner, but easier to cut. Anyway, I measured it up on top of the Spitfire, cut it to my taste, drilled 2 holes, then 2 holes through the Spitfire, and secured with screws and rubber washers. With the now secured visor attached to the windscreen, most (not all) of the wind buffet is not in my face anymore.
However, I created another problem which needed fix'in. With the top of the windscreen re-directing more wind, I found the top wanted to tip back and I was worried with prolonged riding I'd end up with a broken windscreen. My solution (again I will show in picture later), I drilled 1 small hole on each lower side of the windscreen near the front turn signals. I then used a very small bungee cord, hooked it in the holes and then wrapped it around my handlebar.
Reason I used bungee cord is, I take my windscreen on and off a lot depending on where I'm gonna ride and doing it this way keeps the tools and time in check. Tylenol Run trail ride, no windscreen, trip to the store, put windscreen on.