Lower is better for stabilizing and make sure it's not bumping mirror as that would exacerbate the issue. I have mine usually middle of windshield about 1/2 up or occasionally (just for data & not vid) vertical near driver A-pillar.
Also check the s/w for a image stabilization / auto focus feature.
I use Porsche's Track Precision App (as my car is capable) and video is always smooth... once I found those features within.
Good luck and have fun
