Regarless of whether ki actually exists, maybe thinking in terms of ki/extenstion/etc. is the only way to get those body mechanics expressed. In other words, your brain needs that model to make your body get the job done when there really isn't any other vocabularly for it. And if it's that hard to describe, imagine how hard it is to do!
I've personally found that when you repeat something 1000's of times over it's never the same each time, but the doing does kinda get better over time.... nothing mysterious about that.....
It's called adaptability and making use of any given situation....
I practise it every day of my life.....
I assume you do?