You should not set the threshold right at the distance you sometimes measure. You say roughly 91 to open door and 193 to car.
You should set door thresh to half way between open and car, in your case 140 will do.
And set car thresh to half way between car and no car (ie floor) I will guess 360 for you so 270 would be a fine setting.
The idea is if you get a distance less than door thresh it will deduce door is open. If not and it is less than car thresh then it is closed with car. Otherwise it is closed with no car.