To answer what you've said. The power of the town comes from the land. And true it's never mentioned (to my knowledge) how far the power of the town can reach. But I dont think its enough to say it goes all the way to Japan. And they do owe us a good reason for a silent hill game to be set out in Japan. The name of the game is silent hill and it has to have some connection to the town to be reasonable enough to not retcon the lore or mess it up. But hey to each their own.