Having been beaten before, the second time that the Gadiantons attack, they attempt a different strategy. Rather than giving the Nephites time to withdraw and to create a vacant buffer zone, the Gadiantons attempted to siege the Nephites. The text says they laid the siege “round about,” but it is doubtful that they had sufficient numbers to fully surround them. It does not appear that the Gadiantons controlled the north; we will see in a few verses that Zemnarihah will attempt to flee in that direction, but is cut off.
The Gadiantons would not necessarily need much on the east or the west, as the seas were effective geological barriers to escape in those directions. Perhaps this refers more to covering as much of the defended city as possible.