I did it again, as I was driving home in my car I wondered why the hugest of the asteroids in my clone of the Atari Asteroids Game from 1979 not just pushed the smaller asteriods out of the way on impact, I had a revelation!
The mass of an asteriod is not based of a one dimensional diameter like metric or a two dimnesional area like metric for that matter. Mass is mass and it is volume based, so away I went an added a cubicSize member to my asteroid class which is size*size*size, where size is the diameter of the smallest circle surrounding the center of mass of the asteroid. And behold it looks more like the effect i was after, try it out:
It goes to show that the human mind works in mysterious ways when it comes to trouble shooting and problem solving :-)