Originally Posted by macsen rufus
Actually, I think it's a bit more subtle than this - the individual men with the highest personal valour in the unit go into the van. This isn't necessarily the unit leader - I have on occasion put units into wedge formation and the unit flag (which usually hovers over the leader, I believe) has appeared well back in the unit, and not in the van.
Try it out on a unit where the leader has a valour-reducing vice like gluttony and you'll probably see this effect :bow: