The location and/or movement "feel" of #3, is related to hinge type. Because the #3 "senses" the shaft on the angled plane but the back of the left hand (and therefore the grip unless you asjust your grip during the swing) maintains its relationship to the associated hinge. Therefore, only with angled hinging will #3 remain in one "feel" location, behind the shaft, because the clubface retains its relationship to the angled plane.
Which leads to why angled hinging is "best" for hitting and Horizontal hinging is best for swinging, but thats another story.
At address the location of the #3 pp for hitting or swinging using a strong single action grip is the same, on the back of the shaft, perpendicular to the line of the wrist cock this doesn't mean it's going to be exactly at any angle it depends on your left hand impact location. The action of the #3 pp differs from swinger to hitter but both are in the same location at address. the violinist also uses the number three pressure point as he senses the strings angle and pressures.
It'll be located at the lowest point of contact between hands and club , aft of the direction in which the club is travelling. It senses inertia. And is located at the top of the LCOG, the Sweetspot Plane in other words . If you gripped the club cross handed, during Radial Acceleration it'd be located somewhere on inside of the tip of the left index finger.
During a Lagging Takeaway you sense the Lag at the lowest point of contact between the inside of the right hands index finger or thumb and the fore (as opposed to aft) of the handle.... a reverse #3 is you will. The fore of the handle is now aft of the direction in which the handle is moving in Startup... If you know what I mean. Dang .