Earlier quoted context omitted.
I'm talking about the leading edge of the wings, where they meet the fuselage. How far up that is from the tip of the nose is often not based on any existing edge or fold.
The fold that separates the "fuselage" from the wing? Not the leading edge (except in one point), but you are right, that is the one where many otherwise non-arbitrary planes make an exception. My favorite designs, front heavy with a decoratively complex leading edge would usually have plenty of potential guidepoints for the fuselage fold though. Good times, bringing up those memories makes me wonder when exactly I s…
Similarly, you often don't want to fold right to a crease, as it can cause bunching. It's often a better idea to leave a mm or so of extra space for inward folds. Doesn't make the design less pure or anything though.