[speculation]I think grade point gain is proportional to damage taken, but since the grade bonus is related to the inverse of crew size the combat grade bonus gains in 6.x may be higher than in 5.x with the smaller crews.
That said, a +10% grade gain shouldn't happen unless the carrier is actually just 20 guys running a pair of boat bays and a bridge surrounded by 44,000 tons of armor, and even then I'm a little surprised to see a gain that large.[/speculation]