I have two AGV helmets now. The first one was flip face one, AGV Compact Course and now I have the second one, AGV K3 SV. Zero buffeting with both of them but more wind noise now, then with Schuberth.
As for Givi Airflow, the best setup I found is tilted all the way towards the rider, mounted on top holes, sliding screen in the middle of the sliders. Buy the way, I'm 6"2.5.
Givi Airflow uses technology that creates invisible air screen. So, as there are two screens, high pressure is created by the air compressed between those two screens, that is then shot vertically, producing that invisible screen. The bigger the area where two screens overlap one another, the better the invisible screen. As the result of my test, it's not about how much you rise the sliding screen but how big pressure they create. So, to find the best setup for you, you have to play a lot with sliding screen. As I'm tall and knowing that I needed the biggest area possible where two screens overlap, I moved the lower screen from mid to top holes and pushed down the sliding screen a bit. The pressure rose and noise went down a bit.
So, it's just a lot of testing.
Precautions: do not mess with sliding screen while riding. Only if you want to unlock it and hit it a bit to go down. If you try to rise it you may pull it out of the latches and there you have a big problem.
So, if you want to rise it, stop and do it.