Stan explains this very well in a few vids. He demonstrates how obvious it is to recognize which way to pivot/sweep by looking at where the ob would go if you shot it from the fixed cb as seen from the perception. This actually does require a little experience, at least enough to be able to estimate the ob path given a certain cb-ob relationship. Sometimes it's very obvious, other times not so much. Having a good understanding of fractional aiming can make it easier to recognize ob paths based on various cb-ob relationships.
I never think about fractional aiming with CTE.