Hmmm. One could at least approximate engineering attempts on the order of seeding Class II circles, then. Non-performers who improve circle flow (and are therefore heavies even if people glancing in the door don't necessarily recognize them) strike me as a particularly interesting phenomenon.

I wonder if the circle-particle interaction should be modeled as several steps, the way infiltration of a blood borne cell (like a white cell) into the tissue takes several steps. First the blood borne cell is running along down the center of the blood vessel, then it contacts the side and begins rolling adhesion, that is, rolling down the side of the blood vessel, moving with the blood flow but sticking to the side, then it stops rolling and sticks flat to the side, then it oozes through into the tissues. These stages are (if I remember right) triggered by different environmental factors; a cell undergoing rolling adhesion may let go without ever sticking flat if the environment changes

Would circle particle interaction have similar stepwise interactions, for instance first glancing in the door, then deciding to hang around for a while, then deciding to hang around for the long term? Perhaps different factors affect these decisions?