What is the prediction reasoning when the jib is eased or reefed?

"That's a good rule of thumb and will keep you out of trouble. You can also predict from this rule that the fairlead should move forward if the jib sail is reefed. If the jib sheet is eased and the sail goes out and forward then the fairlead should also go forward. But this is a completely fine tuning adjustment and most people, even racers, tend not to bother with this adjustment." I'm am uncertain how the geometric center yields the prediction of the fairlead going forward as the jib is eased (since the geometry of the sail is not changing? Also when reefed it would seem the center moves lower and forward and thus it isn't intuitive to me that the fairlead needs to move forward?