Argumetative but consider this, you have not just one quantifiable skew but a continuous range of skew per the results you desire. And, taking into account the dynamic interactivity of shot making, a lot of options.
Frinstance, say you have lots of slack on the cueball landing but you have difficulty getting your stick into a comfortable position - ball in the way or anything else, chair, pocket liner etc... While you're trying to cinch this shot, you'll automatically be weighing your "is this gonna go?" senses. Chances are if you need english you'll be fiddling with the amount.