There appears to be some confusion about the cause of skating force. If the cause is primarily the cantilever being not tangent to radius of the record (i.e., cantilever to perpendicular to a line drawn from the spindle to the point of contact, then skating force would be near zero at the two null points and would reverse direction as the null point is crossed; that does not happen. Skating force comes from the stylus dragging in the groove. That force is largely along the line of the cantilever (very slightly to the left or right of directly on line when not at the null point). Of course it also varies from directly along the cantilever when playing different parts of a waveform, but still, it is primarily along the line of the cantilever. The drag is pulling the cantilever. If the cantilever is pointed directly at the tonearm pivot, there would be no left or right bias to such pull. But, that is not the case because the headshell (and therefore the cartridge) is at a very substantial offset angle and points far to the right of the pivot. This is the cause of the skating force.
You can demonstrate this for yourself by pretending your arm is a tonearm. Put your elbow on a table (this is the tonearm pivot. Hold your arm and wrist straight out and now pull on your middle finger (this is the equivalent of drag pulling on the stylus and cantilever). Your arm should go nowhere. Now bend your wrist at an angle (like the kink in your tonearm) and pull straight back on your middle finger. Your arm will move inward, just like a tone arm does when tracking a record.
Ledermann's technique is not meant to exactly simulate skating force drag. It is something he developed as a proxy for roughly estimating the amount of antiskating force that should be applied. ALL approaches are just rough compensation, which is better than nothing, but far from perfect. It is also very easy to apply. He makes the case that using test records to find the point where the cartridge mis-tracks in one channel to determine whether to apply more or less antiskating force optimizes the setting only under extreme conditions, but, those conditions happen very briefly so the rest of the time one is applying too much antiskating. I think his approach makes sense. A similar approach is suggested by a cartridge manufacturer (I think it is Lyra) in their set up instructions. They recommend looking at a cartridge from the front and then cuing the arm down to a groove near the center of the record; at the moment of contact, the cantilever will briefly skew inward or outward; if it skews inward more antiskating should be applied.