The assumption of 30% seems valid in light of police statistics showing that around 30% is the "average hit rate" - which includes: people, dogs, cats, and automobiles.
What seems skewed in the analysis is that the avererage number of shots fired. I have seen a statistic giving 8 shots as the average amount fired during a shootout for the initial exchange. Shots fire after that seem to end at 13 - 15.
So, given lies, damned lies, and statistics - apparently, if you can survive the first exchange of 8 shots, you may need 5-7 additional shots. What that means is that unless you're carrying a gun with at least a 16 round capacity magazine, you're going to be reloading regardless of whether you are carrying a gun with an 8, 10, 12, or 13 round magazine.