Density means weight. If they move density outward, then it raises the RG numbers, while moving density to the center should lower them.
That is why a picture of a core can be deceiving. They can create all different shapes to capture the imagination of bowlers, but ultimately where the density lies is where the core will have it's most influence.
In lighter balls (12 & 13) Brunswick, for example, uses a core that will perform and allow the ball to be "close in reaction" to the heavier balls. They have 2 versions with one being symmetric and the other asymmetric.
One may ask how is that so? How can a "generic" core do that? Well, first in importance to ball reaction is what the bowler does to the ball (speed, revs, rotation, tilt, etc. Second is the ball's cover and it's characteristics, and third and fourth are the core design and layout.
Have you ever asked yourself why it is that you generally play in the same area on the lane (assuming fresh oil) regardless of which ball you have in your hand? The answer is in the previous paragraph.
