PDC Aftermarket License Plate Kit

Dealer installed Park Distance Control BMW Part # 66210395009 Module which mounts on the rear license plate of my 2010 525i. Initially the alarm sounded continuously as soon as the car was put into reverse. A follow up trip to the dealer discovered the unit was installed too close to main power feeds which were causing feedback and keeping the unit on. Now working OK, but I was wondering if anyone knows the range of these units.? Previously I had a 3 series with PDC factory installed and it seems the operating range was much longer. This new system only starts beeping when an obstacle is about 3 feet from the bumper. is that normal? Can this distance be changer to make the unit more sensitive?