Whatever side of the track the pin is on, i.e. positive or negative, the pin migrates to that axis. This is why the track migrates the way it does when it flares. If you place a pin on the negative side of the track, similar to a full roller layout, for a 3/4 roll, the track flares over the gripping holes. Why? It is migrating towards that axis.
Pin to PAP distances dictate flare as well as ball motion. A pin at 3 3/8" from the PAP is the highest potential for flare. Moving the pin either towards the PAP or the track decreases flare potential as well as shape of motion. A pin closer to the PAP will create an earlier smoother motion vs a pin closer to the track, which will create a later & quicker motion.