...the key concept seems to be "about one third."
In gross (the precise numbers are something that Okumura Jun could work out in his sleep) the prefectures hosting only a third of Japan's population will be providing two thirds of the local party organization votes for the Liberal Democratic Party presidential election.
In gross, the single seat districts and at-large regional bloc Diet seats producing less than a third of Japan's economic output will be providing over two thirds of the Diet member votes for the LDP presidential election.
In sum, in the selection process for a new party president--and by extension, a new Prime Minister for the Land of the Rising (?) Sun--the forces of regression will outnumber the forces of change two-to-one. About one third of the party votes cast will be representing nobody and nothing.
And in the rural-urban differences debate, the LDP is supposed to be playing the role of the party of the rational good guys and gals!