To a certain extent, this was implemented in the MTW already. It didn't work always, but the idea was there... This feature has not been implemented in RTW though. Interestingly enough, the "do not shoot into the backs of your own troops unless ordered to" feature was not present in Shogun either. So, is RTW, in a sense, a step back to Shogun?

On another note, the same archers that are more than happy to shoot your own troops in their backs would not shoot an arrow if there was a SINGLE tree between them and the target unit... Happened to me while attacking the Selena settlement: in their city plaza... The flag pole was between the archers and the target unit: the archers would just stand there and do nothing: put them on auto-fire or give them a specific order to fire: nothing... I checked, the arrow cursor did turn green above the enemy... Once I moved the archers to the other side of the pole, they did their job.