Cars but no people

We have had our Ring 2 doorbell for almost two months. We made adjustments to sensitivity several times but continue to experience motion detection of the car or truck in the street yet the pizza delivery person can approach our door and we get nothing until he is about halfway down our driveway heading back to his car. Sometimes we get people as they approach the door but many times it does not start recording or alert us until they are on top of the doorbell or until they leave. We have had people come and go with no detection at all. Any thoughts would be greatly appreciated. Thank you.