Some archers did have quivers on there back. It is simply better for archers that stand firmly or their feet shooting very heavy bows. I agree that you should be able to put them on the hip, AND in the back. It is simply more realistic. Beside, there WERE mercenaries (germans I think) back in the day who would use crossbows with two handed swords and a kinda half plate armor. Heavy xbowmen basically. It would be great if you could reproduce this in game ! And yea, having a pavise in the back is also a thing : Some crossbowmen would even keep them on their back during the whole battle, so they could turn around while reloading, and be covered by their pavise shield