How fast do you need to go to beat the speed trap

if a truvelo speed camera is facing away from the direction your driving,and at an angle, not perfectly forward, does it capture cars on the opposite side of the roads or just those coming towards it?

I notice that cars often brake suddenly on clear roads because they detect a speed camera or those white line things, which surprises the driver in the car behind who then brakes and swerves, sometimes causing an accident

I live and work in China where they now using cameras to detect speed. This is very effective as the police here tend to do nothing at all, so automated devices are the only means to catch speeding drivers who tend to drive poorly at any speed. I was told that the lisence plates have a focal point, which I do see on my plate. It is a recessed dimple about one quarter inch in diameter and it appears to be a different alloy, but it may be my imagination. It is NOT, painted for some reason, and most are rusty. There is definately some reason for the dimple and the fact that it is NOT painted. Many people here completely paint over the entire plate to hide the white numbers from the camera. I am not sure if it works, but the local police do not seem bothered by the fact that 30% of the cars have lisence plates with hidden numerals. Just curious how these cameras focus and what the technology is regarding the dimple in the plate.