I'm afraid that realism as a motivation is completely out of question.
It's not realistic for archer units to fire at a few scattered routing soldiers when the bulk of the enemy's army is advancing upon them.
It's not realistic for archer units to shoot their own troops in the back on purpose; sure, accidents do happen, and occasionally there should be losses to FF, but certainly not as many as there currently are ! As you guys pointed out, it was just fine in MTW when they wouldn't shoot on their own if they risked killing friendlies, but they would obey your order if you explicitly told them to. _That_ is more realistic, not drunken archers shooting at whatever is in front of them regardless of colours...

And what's up with those trajectories anyway ? I can accept more friendly casualties from slingers, but unless the enemy is literally up your ass, arrows should always go _waaay_ up, not in a straight line...