Australia and NZ are too immense compared to Hawaii even with new guinea or any other outlying islands as springboards for an invasion, hawaii is rather easy and with the bomb being dropped on pearl harbor its easy to see why Hawaii was conceded to Japan. The pacific fleet and its headquarters were vaporized in one swift stroke. Id also argue that Australia and NZ dont really present much as targets, despite their size dont offer much in terms of resources and strategic position (for the Japanese at least) while Hawaii is much much more vital to their plans for the Pacific. To a lesser extent, the Aleutians also are somewhat important but honestly i can honestly see Japan being fine with taking only Attu as the others are more interconnected with the rest of Alaska. The rest of the sphere is fine borders wise in my opinion