Head design and weight distribution determine Center Of Gravity (COG) position. It is simply a balance point.

Iron manufacturers attempt to place mass as low as possible for "low COG", to generate higher ball flight and backspin.  I believe the same physics applies to putters, except that it should be reversed. This is based on the fact that a putted ball, which remains in constant contact with ground surface, needs to quickly achieve a fully forward, or "true roll", by overcoming the effects of rearward rotation created by loft at impact. 

The cross section of both Gaim putters shows that 75% of the strike zone's mass is located in the upper half of the head.  The A-365's high COG combined with a 3.75° loft has been robot tested and proven to beat putters with high "true roll" performance.