Don,
It is a fact that to pass a UL test for an AIC rating the breaker must protect 10" of rated conductor as well as itself.

The quote I provide is:
from
IEEE TRANSACTIONS ON INDUSTRY APPLICATIONS, VOL. 35, NO. 1, JANUARY/FEBRUARY 1999 page 135

titled
Short-Circuit Ratings and Application Guidelines for Molded-Case Circuit Breakers

written by:
William M. Hall, Senior Member, IEEE, and George D. Gregory, Senior Member, IEEE