As long as you are handy with fabrication you may want to try making something like this:
This is a photo of Aeroflow's Aeroguard for the 950/990. I've been running the stock screen with these and never experience buffeting. For reference I'm about 6'2" and have Seat Concepts stepped seat that drops me down and inch or so. I wear a Shoei RF-1000 helmet. Height and distance behind the screen will be a factor to where the airflow hits the helmet, if at all. This is what makes troubleshooting this buffeting issue so confounding.
I think the Aeroguards keep wind from coming up behind the stock screen and creating that oscillation that we feel as buffeting.
Anyway, after doing an exhaustive evaluation of several of the Aeroflow screens that fit over the OEM windshield, both with and without the Aeroguards, in the long run I've been most satisfied running the stock screen and Aeroguards for everything other than long-distance highway touring where the larger screen offers a slight benefit by getting more wind off of me and being less fatiguing on those 400+ mile days.
If you like the looks of the OEM screen, I'd suggest building something to block that troublesome airflow at the point shown in the photo and see if it eliminates the problem for you. Changing the screen size and shape only may not be the best answer.
For those who don't want the hassle of fabricating, just get the Aeroguards from Aeroflow and avoid the time and effort.
Either way, I think this is a solution that will directly address the airflow problem in a way nearly all the myriad versions of screens don't.
I hope this helps and best of luck with the project!