I use opengarage so have been using ultrasonic for a very long time. I dont get an issue with false feedback. To give you an idea on accuracy, have a look at the stability,
You can see car briefly out at the start, car in for most of it, and then car out again, followed by 1 reading where it picked up the garage door open (it’s covered by the panel lift door when open).
In a garage like mine, the door pivots and is horizontal when open. A distance sensor on the ceiling can therefore show whether the door is open, as well as whether there is a car there (when closed!)
It’s 3 states with a distance sensor on the ceiling. Too lazy to convert to cm, but here’s the idea in feet:
If distance is like 1 foot: garage door is open. (We can’t see if a car is parked or not because the door is in the way)
If distance is around 3 feet: garage door is closed and car is parked under sensor.
If distance is around 8 or 9 feet: door closed and car is not in garage.
I achieved all this with template sensors based on the distance in cm but then I moved homes and let the config blow to the wind. It’s in a thread here somewhere though.