When a skirt covers the knee when sitting, it will also cover the knee when walking up the steps. And regarding getting into a car, it’s not the extra inch in that will cover the knee (obviously, I’m talking only about the legnth of skirts that cover the knee when sitting), but the width of the skirt is what makes a difference.
So too, on a windy day, it’s not the extra inch that makes a difference, but the cut (gathered cut) and weight (lighter fabrics pick up easily) of the fabric.
That’s why I say, you can’t be too technical, you need some common sense.