I think I just had a breakthrough ... 10 successes in a row making my kick sensor work!! After months of Python levels of silliness, humiliation and abject failure.
Here's my "method". Stand a foot away and square on to the 8" sections of your car's back end/tail lights that are just outside of the tailgate, but still behind (vs. to the side of) the vehicle ... i.e. to the inside of the corners. Give a small kick that lifts your foot off the ground only a few inches. If I get close to (or worse, touch) the underside of the bumper it fails to work. Kick straight forward, not side to side at all as long as you're standing square to that small section of the car. Kick once, and wait a second for it to work. It's no faster to respond than the radio.
Good luck, chaps!