What does "Negbah" refer to?
Bi'ur ha'Gra: It is south of the Nachal.
Was Yisachar to the east? Was not Efrayim east of Menasheh?!
Metzudas David: Yisachar was by the Yarden.
Bi'ur ha'Gra, Malbim: From Michmesah, Menasheh's border jutted out to the north of Efrayim's. At that place, Yisachar was to the east.