As mentioned above, the motion detection is generally better at capturing side to side motion. Careful camera placement can improve motion detection, take a look at the following positioning tips for best performance: How do I position my Arlo Pro 2 camera?
I understand how the camera works. See the attached picture. The red area is the tiny area that sets the motion detection off when a car goes by. The blue is the entire length of the driveway and porch area that only selectively goes off. If the camera is inconsistent then it is pointless, because as I said, when I actually needed it, it was no help at all.