'When bad things happen to broken units, tonight on Jerry Springer...'
Sometimes them's the breaks, so to speak. On the other hand, if there's a good reason to stack multiple leaders then you shouldn't fear the dice.
I find that I usually don't have so many leaders that stacking them in the same hex is an issue. When I do, I usually have something in mind that will reduce the concentration of leaders, such as shooting with one and moving with the other. If they've broken and have routed to the same hex, I try to make sure that they've found some place either where they can't be hit, or can't be seen, or hopefully both.
That can't always happen, but I've been in very few situations where I had to stack leaders.
You take your chances in this game, but you learn when not to take them after a while.
Now, if I can only learn to follow my own advice.
NP