Ah, but for every logical explanation, there's an almost-exactly opposite, equally logical explanation....
1) They expect us to to run to our city, so we'll throw 'em off and run to the open fields to the left.
2) They've cut us off from our boys that-a-way, so the only way we can run is to the open fields to the left.
3) Those mountains look inviting, but I don't think we can climb 'em fast enough. We better try hiding in the open fields to the left.
3a) Those mountains would be great but we'd visible for 100 miles as we were trying to climb -- our only prayer is running left to the fields where we can maybe duck out of sight.
(and others)
Now, a lot of this is said tongue-in-cheek, but there's a nugget of truth there, too. Retreating as a cohesive unit is hard, especially when you're being pressed. And with the abstraction of combat (which I like), we can never know what caused a local colonel/general/commander to run the way he did, but I can accept the abstraction as is...I even like it, as I view a defensive retreat as a victory regardless -- at least they have to burn two units to kill my guy.
And while I also have a tendency to agree on the river thing, there's a flip side to that coin, too.... "Let's get across this river and then burn the bridge behind us."
Arathorn