I was told directly from a sheriff friend here in Southern California that they aim their radar guns at the front license plate, so the lower your detector, the better off you'll be in picking up the signal.

I have mine mounted where the sensor is just above the windshield wipers and I've never had a problem. I normally pick up the signal around corners as well.

I guess if it's illegal to have one in your state then mounting it up high is the only option.