Missile units and "friendly fire"?

[Quillan]

With regards to the "flat trajectory" missile weapons, I can't help you. I'm still playing my first campaign, as Byzantium; no crossbows, no arquebusiers, no muskets, no cannons except bombards. Bombards WILL fire through friendly units if things are in the way. From being on the receiving end of crossbows a lot, it looks like the game has them fire in a more arched trajectory, similar to bows.

[katank]

If xbows arc their shots, they lose a huge amount of damage. Even regular archer units benefit greatly from being out front. So put your archers just ahead of battle lines and retreat when threatened. It's more micro but it's more efficient.

As for flanking with missiles, it can be useful at times. Often arcing fire arrows in concert with flanking infantry and cav is more than enough to break the enemy. If they still last though, pouring missile fire into their back can be amazing especially with javs or gunpowder units. Also note that missiles often fall short so you may want to target the middling units in an enemy formation instead of frontmost.