Motion sensor fails to work correctly

I have a new Ring Doorbell 2 and I've been playing with the motion settings for a couple weeks to get it right, but it keeps giving me late or false alerts. My house faces the street -- it's a quiet residential road in a small town, not a busy highway but we get a few cars. So I rolled back the blue dome sensor to cover ONLY my porch and front step. I made sure not to get into the road. Still I get alerts when cars drive by, and I DON'T get alerts on my porch until the person is standing right at my door. I need to get alerts when they come to the steps, not when they're already at the door. By then it could be too late to stop anything. Also, today I got an alert when a car went down the street. And I noticed there was a car parked in front of my house between my camera and the street. So apparently I got an alert when this car drives by but I did NOT get an alert for the car that came down the street and parked in front of my house. It's really weird. How can I fix the setting to alert when people are on my steps (6-8 feet away) BEFORE they get to the door, but NOT get alerts for passing cars (which are 15-20 feet away)? I've also found the response time is REALLY slow when I go to look at my video. I get an alert and it takes me 30 seconds to load it on my screen. A lot can happen in 30 seconds.