When you are targetted by an enemy missile unit you get the morale drop m8, not when u suffer lost from friendly fire.
So in melee the enemy has a -6, while your troops no. This is the reason musks are still usefull with rain.

When the enemy charges I always move the spears, never the musks (the hold formation is important). This is because I don't want the enemy targetted units to increase the morale. If the enemy has musks aswell it's important to take care of the ricochet, but if it has only arrows, the ys could be deployed really close to the missiles.