MilozFolly, for me, on my 650 L2, higher was not the answer. I eventually had mine on a low setting. The bottom screen in the middle & the top screen as low as possible. I also fitted different mirrors & mirror extenders, but they only made a minimal difference, it was the low screen that sorted the buffeting for me.
The Givi Airflow works on the Venturi effect, meaning the more the two screens overlap the better.