You are right there as far as understanding how the mass bias works. You seem to understand why weight holes work. Mass bias is simply a hole in the core that maximizes the differential between the height and width and centralizes it to one axis. (Most times it is not a hole in the core, but the core is wider on one axis than the other)
Draw a line between the pin to the mass bias. This is the line of most resistance. When your PAP is on this line, it is experiencing the most resistance to revolution. As your PAP migrates towards this line, this resistance to revolution grows. Once your PAP crosses this line, it revs easier. Therefore, putting the mass bias close to your VAL lets you cross this line earlier on the lane, causes the ball to rev easier, earlier. Putting the MB further from your VAL delays when the ball starts revving easier.
One caveat: perpendicular to the mass bias axis and the line of greatest resistance through the pin is the line of least resistance. This line crosses an axis 6-3/4" from the pin that goes through the widest part of the core. If your PAP approaches this line, it revs easier and easier until it crosses it. Then it resists revving. This is why you don't put the mass bias in your track. With the mass bias in your track, the line of least resistance is close to your PAP. Your PAP will actually migrate backwards towards the line of least resistance, creating negative flare or flare towards your grip.
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Where is the bait? I'm goin' to jail!!! - Chocolate GAYzer