If archers/crossbow units marked as medium infantry cant cross the billmen/pike lines and cant shoot over friends heads.... and dont talk about that this units after shoot cant move!!!!!! another question is why not add a limit of shoot to this units and a resuply unit for this units.
I've found it quite easy to have heavy foot behind the archers and if you leave some gaps its easy to pull teh archers out and put the HF through to the front line.
My main issue is the MF archers being too manoeuvrable. We're working on various ideas to solve this.
The problem is that you need move the HF when were the bow units who retreat behind the main line because not allways is a good choice advance the line of pikes and if your bow units shoot cant move and they are medium infantry... well, at least i see this units do better than pike units