Hmm... guess his ring 10-16 fix really did implement the arbitrariness we requested.
Circle Radius is absolutely related to the x,y coordinate system (not the in-game "hex" coordinates). In classic Aaronspeak, the values actually refer to diameter, however. Without modification, it translates to 180 to 200 unit radius from hex 0,0 (Ring 1, stars), or 9-10 hexes. If you look at the Asteroid Belt system, you can see how the "Circle Radius 200, 240" positioning translates into about Ring 5 to 6. The diameter of the circle created by the asteroids is somewhere between 200 and 240.