Most states falling below the green line tells us exactly what?
Perhaps the relationship doesn't hold when the number of counties/district is low. If you start from about number of counties/district is around 10, you could drop the green line down, and reduce its slope a bit.
If the average number of counties is small, you may have areas where the number is much smaller, or alternatively where the counties are somewhat large relative to the congressional district size. In Iowa, it may be hard to create a district with less than 15 counties (Davenport, Dubuque, Iowa City, Cedar Rapids, and Cedar Falls, perhap?).
More counties gives you lots of flexibility. Compare northern L.P. Michigan to the area along the southern border. There are dozens of choices in norther L.P., and if you were willing to give up on erosity, you might be able to get a deviation comparable to Iowa. But in the southern area, there are very few options.
