Where exactly is "Midbar Tzin al-Yedei Edom"?
Rashi: It is at the south-eastern tip of Eretz Cana'an, at the foot of Yam-ha'Melach, with Mo'av beside it on its east. 1
East of Edom and south of the lands of Sichon and Og. Ha'amek Davar: This is difficult, for I proved (21:10) that Edom is on the eastern edge of the southern border of Cana'an - at the foot of the Yam-ha'Melach and westwards - whereas Mo'av was situated at the southern edge of its eastern border - next to the Yam-ha'Melach and northwards!