Questions about the physical gps antenna

Hi
I just loaded InstaMapper and it works great. I have questions though. First off, where is the gps antenna located on the storm? Basically, if its in the belt holster, in the car, is the portion of the phone sticking out the top with a view of the sky the same portion that holds the antenna? Does it even matter? will the gps antenna track through the holster? I guess I'm confused as to why the antenna will track through the plastic housing of the phone but not through other physical objects. Its just helpful to know also if I look for a car cradle (so I don't get one that blocks the antenna).
Thanks!
Mike