Perspective is important.
Dear Math-challenged editor:
I realize that 11 is only 2 more than 9. But another way of looking at it is that it is 22% more. I only have 3 managing editors. If I had 22% more managing editors, that's two-thirds of a person.
Eleven isn't an unacceptable number, but it does almost require an addition to headcount. It's not "the same" amount of work as generated by nine books. It is a significant amount more, and we are not unjustified in noting that it is a burden for my department to deal with.