Iphone mount / sat nav signal

Hi all i need a mount for my iphone and was looking at a brodit, thing is i use my iphone for my sat nav with tom tom, in my old car (insignia) if the iphone was low down anywhere near the radio the sat nav wouldn't get reception.
Anybody have the brodit that goes to he left of the radio above the cup holder? And does the iphone suffer sat nav reception probs mounted there?
I would prefer that mount as its descrete and angled toward the driver, the brodit mount that clips around the air vent is flat and im not sure i could see the iphone screen from that angle.

Any other suggestions/recommendations

Cheers

Dave.