Those quoted leads are the "true" leads as determined by a little algebra.
The leads you're referring to with different shooting methods are the "perceived" leads. Very much analogous to the differences between "true" recoil and "perceived" recoil that facinates certain members no end.
This is all very true. If for instance you calculate the lead required for a 20yd skeet target & come up with say 4 ft, shooters using; swing thru, constant lead or spot shooting would have three different perspectives of "Perceived Lead". The fact remains though, assuming each centered the target when the gun discharged it was in fact pointed 4 ft ahead of the target. The main problem comes in when people start "Perceiving Facts" that are a mathematical impossibility, which is in fact the "Vast Majority of Perceptions".
For instance if a swing thru shooter "perceives" his actual lead of 4ft as only one ft, & then changes to a much faster load which cuts the 4 ft by 6", & he then "Perceives" his lead as 6", he "Perceives" the faster load cut required lead in half. This of course would be no where close to an actual "Fact". The fact is of all the factors involved in his perceived lead ie personal reaction time, action time of the gun, ignition time of the shell, bbl time & time of flight of the shot, he has changed only one. In fact he would not have cut his lead by 50% but 12.5%.
Yet he may well loudly proclaim the "Fact" that the faster load cut Lead in half. He may be considered a very "Accomplished" shot & knowledgable shooter, but if a sustained lead shooter, based upon his "Perception" adopted the faster load & cut his lead of 4' in half to 2' he would have a very sudden "Slump" in which he would miss everything he shot at. "Perceptions" "Must" be individually adopted & are very seldom actualy "Factual".
