I have the Roady 2 in my vette ("03 coupe) and the Sky-Fi in my daily driver. In the vette, I have the antenna mounted (magnetically) to the inside metal trim around the rear window. On my daily driver the antenna is mounted (again, magnetically) on the front center of the roof.
Here's what I've noticed about reception: In the vette, when I drive down a tree lined road, reception is fairly lousy with the signal going in & out and eventually losing the signal altogether.
In my daily driver, I can drive down that same tree lined street, and the reception is great!!! In fact, in this car I have rarely lost the signal at all. The vette is another story.
I'm not electrical engineer, but is it possible that an all metal body car helps reception???