You can put it anywhere theres a smooth surface. I have put it on the outside of my door at 90+mph...on the hood...on the windshield...on the back window at any height.
here's one where I put it lower.
http://www.youtube.com/watch?v=ADJ4H...e=channel_page
I know I wasnt being smooth, I wasnt trying to set any records and was unsettling the car on purpose a lot to see how it handled it.