The image below is mathematical proof that the volume/mass of frustums are not proportional to distance.

What this means is that the mass per unit area is not equal for the segments (see post

#100) which means that the gravitational influence upon point "P" differs for each segment of a cone.

The reason the volume/mass of frustums are not proportional to distance is because of the centroid of the triangular portion of each segment --- it is a constant r/3 and by definition constants are not variables so adding a constant to a variable eliminates the proportionality.

The math below is the application of

Pappus's centroid theorem for determining volumes.