I'm surprised that tucking in doesn't quieten the buffeting, when I had a curvy it used to be very quiet when tucked in (but I am vertically challenged).
Assuming it's turbulence that's causing the problem, there's a US company called Laminar Lip whose aerofoil/spoiler is supposed to stop turbulence. I don't think they have a UK dealer so you'd have to import one yourself and pay the duty - which works out expensive.
https://www.laminarlip.com/sv.php
Being a tinkerer, I'd be experimenting with making spoilers myself to see if I could fix the problem. I suppose you could remove your existing screen temporarily and see what difference that makes.
Having seen your pic I now understand why tucking in doesn't help
It looks like the screen is directing the airflow straight to your helmet.