Positioning units for bridge defences

[caravel]

As I said, it seems to happen most in bridge battles (when I'm defending), where it's enough to make me pull my hair out. At first I thought they might be trying to get disentangled from other formations - I do tend to stack the units pretty close together, and all in loose formation - but they often get themselves even more jumbled together, so it's a terrible job if that's what's happening. Can someone enlighten me as to why they do this and how I might stop it, or at least manage it in a fashion that's not like a game of "whack-an-insubordinate-mole"?

It's most likely that your units are too crowded. Units in STW/MTW will not intermingle unless they are actually engaging an enemy unit in "engage at will" mode. The units will try to stay in distinct blocks at all other times. It's common near bridges because it gets crowded more easily there and you cannot actually deploy right up to the water's edge. Try not to position your units so close together and keep them back from the bridge. You generally only need 2 or three defensive units directly in front of the bridge. Naginta or YS are good for this role. If you place them too close during deployment they will move out as soon as the battle starts - this can be disastrous.

How are you positioning your units? I tend to favour click and drag selection to get my units positioned both before and during battle.