Even though it was for different reasons, sieges always were a nightmare for both sides in the conflict. That was most likely the reason behind the local lord's strategy. Instead of enclosing his entire army within a single area and risking starvation, he decided to give Fen's forces a battle right outside of a small valley that they had to go through.
Basing on pure strategy, this move was counterproductive. With how relatively narrow the passage was, lord's forces could only use a small part of their questionable strength, allowing the mercenaries to thrive.
Yet, once human's psyche came to play, this was one of the deadliest traps that Fen has ever faced in his short history as a mercenary. Surely, with the insane difference of personal fighting ability, the veterans wouldn't have any problems dealing with any number of opponents they would face in this scenario… But…