C. F. Keil and Franz Delitzsch on Joshua 16:9

Jos 16:9

The tribe of Ephraim also received some scattered towns in the territory of the tribe of Manasseh, in fact all those towns to which Tappuah belonged, according to Jos 17:8, with the dependent villaGes.The reason why the Ephraimites received scattered towns and villages in the tribe-territory of Manasseh, is supposed by Calvin, Masius, and others, to have been, that after the boundaries had been arranged, on comparing the territory allotted to each with the relative numbers of the two tribes, it was found that Ephraim had received too small a possession. This is quite possible; at the same time there may have been other reasons which we cannot discover now, as precisely the same thing occurs in the case of Manasseh (Jos 17:11).