I had lots of buffeting on my Springfield but the JESCustoms lowers fixed it. I suspect your seating position with the extended reach seat is an issue. There are aftermarket screens that have a turn out towards the top and it takes the air higher over the rider's head, that might help.
When I had the Scout it was the same problem. I cut a slot in the windshield and fitted a vent from a Goldwing, thinking it would balance the air pressure, but it didn't do anything much at all and wasn't worth the work. What worked best on the Scout was adding a piece of plastic at the top that sat on a couple of wedges of foam that held it out to mirror those flip shields. That lifted the air a bit higher. Here is the vent. First, the hole I cut in the shield. And with the vent in place. I had to cut the vent so it fitted between the handlebars. There is a flap on the inside not shown in this pic. I don't have any pics of the piece I added at the top, it was not the most attractive thing but it worked in a half-hearted way.
From Woodrising (no, nobody else has heard of it either) Rides a Springfield Dark Horse