We have ours (Garmin GPS-57, so pretty small) just to the right of the dots and about 2" down from the top (ours is a 2017 Expy and don't know the dot patterns of earlier models). It sits mostly behind the rear-view mirror from the driver's perspective.
Yes, a dashcam will 'see' the dots and they'll look blurry on the videos. Our placement removes most of them from the view.