If it wasn't still pouring with rain in Mid Wales, I'd crawl under the car and have a look for you.
But, here's a theory.
As the inner cable is pulled maybe it straightens the cable slightly thereby shortening the distance overall and as the inner is fixed the outer would have to move as the shortest distance between 2 point is a straight line.
Only a theory and if the cables are already straight then that theory goes straight out of the window.
