Halfway back along Kyushu's west coast, Kumamoto is an old castle town that was of considerable importance to the Tokugawa shoguns as a counterweight to the presence of the annoyingly independent Shimazu clan down in Kagoshima.
In Kagoshima, there is an independent clan called Shimazu.
According to the graph, the postal service's profit level declines until it is back at breakeven at discount of about 4.5a.