1)
What are the connotations of "Vayitzb'u al Midyan"?
1.
Sifri #1 (citing the Chachamim): It means that they surrounded it (the town) on all four sides.
2.
Sifri #2 (citing R. Nasan) and Targum Yonasan: It means that they surrounded it on three sides - to give the enemy the option of fleeing.
1
1
See Torah Temimah, note 9 and Oznayim la'Torah.