Does the mass bias preceed the pin to pap placement?  Is the major factor in ball reaction the MB or pin in asymetrical balls?  Lets say you have a ball any ball with the .5in away from the thumb in the strong position, and the pin is 2in away from pap.  The next ball the mb is is .5 away from the thumb, and the pin is 4 in away from pap.  Would they have the same reaction.
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i am not an expert by any means, but it seems that the pin is in fact the most important.  Since it is the part of the core that is closest to the cover of the balll, the shorter the pin-pap distance, the earlier the roll, and the farther away the most length.  The MB is somethign that can fine tune the reaction, along with x-holes, so the MB .5" away from the thumb in the strong position will exaggerate the reaction depending on where you put the pin.

Not to hijack, but x59 you're not correct. You said that the pin is the part of the core core that is closest to the cover. That is the definition of mass bias; that is the mass of the core or weightblock is biased at that point toward the surface of the ball.
 Osku, it's been said but bears repeating. They work hand in hand. Below is a little excerpt from http://home.mchsi.com/~s-cross-7-28-71/FAQ.htm

AFFECT OF PIN PLACMENT
Pin to PAP distance:
0" - minimum flare potential, core is in it's most stable position, earliest roll with smoothest arc.
1 1/8" - 1/3 of flare potential, stable core position, earlier roll with smooth arc.
2 1/4" - 2/3 of flare potential, semi stable core position, early roll with strong arc.
3 3/8" - max flare potential, most unstable core position, medium length with the most hook potential.
4 1/2" - 2/3 of flare potential, semi stable core position, late roll with flip/arc reaction.
5 5/8" - 1/3 of flare potential, stable core position, later roll with a flip reaction.
6 3/4" - minimum flare potential, stable core position, latest roll with strongest flip.
Remember : These reaction charcteristics are all relative to the conditions they are being used on and may not perform as expected due to burning up too early or not setting up early enough.
Pin to grip center (GC) distance: The higher the pin above grip center the more lenght you will get fot given pin to PAP distance. The placement in relation to GC also affects where the tracks of track flare intersect (bow tie). Higher pin = Higher intersection. For this reason they suggest high trackers place the pin higher above GC to reduce the risk of flaring over the finger holes.

AFFECTS OF MASS BIAS (MB) PLACEMENT  
As the angle goes from 75° (strong/flip) to 0° length will be reduced and have more of an arc reaction. From 75° to 105° lenght will increase and have more of an arc reaction. Beyond 105° the reaction will keep a very similar reaction but with more length.
Remember : These only enhance the characteristics of the given ball and Pin placement and the flip (strong) position may not necessarily have the biggest backend reaction on given condition due to many other variables that affect ball reaction (bowlers specs, lane condition, etc.)