1)
What is "Matzuk mi'Tzafon"?
1.
Rashi: It is sloped and ascends on the north, towards Michmash.
2.
Radak citing Targum Yonasan: It overlooks [Michmash] from the north.
3.
Malbim: [The one near Geva,] its north side was smooth. It was impossible to descend. Likewise, the one near Michmash, its south side was smooth 1 , and impossible 2 to ascend.
2
If one cannot descend or ascend, we must say that Pelishtim intended to go around the canyon in order to attack Yisrael. Perhaps they camped here in order to frighten Yisrael, and to be able to see what is happening in Geva. (PF)