It is saddening that no game I know has yet represented asteroid fields in a realistic way. That is, rocks with maximal diagonals exceeding the hundred of kilometers and spaced at more than thousand of kilometers from each other. Admittedly, that would be very boring.
I'm not saying your-usual-tighly-clustered-asteroid-field is not impossible, it is just statistically very uncommon because that is an extremely unstable situation.