The distance from the antenna (5 feet is a lot) means that the antenna will not make any noticeable difference to your reception. Couldn't even be an effective ground plane like that.
Offtopic but, I always find it interesting when I see vehicles with 10 antennas on the roof about 3 inches apart. I always wonder if they end up making essentially a Yagi somehow with metal so close. I suppose not since they're all grounded... but it's funny to imagine.