Although everything in the previous post is spot on, from a layman's terms, when I had my stuff with the mass bias in the track (usually just to the left of my thumb - right handed) the ball would not have a hockey stick shape and would be a smooth arc.
Generally, the closer the mass bias is to your track, the smoother the ball, closer it is to your PAP, the sharper the backend. That is a very general-loose statement.
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