Interesting, as most in the industry calculate with a blanket 5 crew per shorthaul aircraft factor. Some do even get away with 4 crews, but that is usually with somewhat less dense operations. But i suppose the difference is that standby coverage for just one aircraft might skew that a lot, whereas in a fleet one standby crew is usually covering for quite a lot more than just one aircraft. Although EASA FTL really requires two sets of standby crews to cover a whole day.