The OEM version, on at least most models, has sensors spread across the bumper. This gives a much wider and probably deeper coverage area than anything you could put just on the license plate holder because they are aimed straight back. I'd be really surprised if you could get it any better than it is with the add-on system. These things are ultrasonic (as opposed to optical or radar), so the only interference that might show up is if it was aimed incorrectly. If it points too far down, rather than out, that would affect it's ability to work (could have been reflecting off the bumper) as would too far up where it may have been reflecting off of the trunk lid or trim pieces. I think mine starts to alert when it's around 5', but don't quote me on that!
Last edited by jadnashuanh; 12-07-2012 at 05:00 PM.