defector

At speed the wind deflector on the Spider vibrates or flutters. It looks like its not actually fixed at the bottom. Has anyone else noticed this and found a cure?

I recently bought the wind defector from Classic Alfa and was about to try to fit it. However the instructions are slightly ambiguous as there are potentially 2 bolt positions (see attached photo) which the bracket which attaches to the wind deflector can attach to. Should I use the top one or...