I remember in BoA it didn't matter if you were in a defensive or passive
stance while in a fort as you rightly received no ill effect should it come
under siege or assault it was used simply for prioritising replacements.
However now we have the cohesion rule and a +1 advantage to being in passive to recover cohesion there should never be any reason for units in forts to be in anything other than passive stance (unless you do not want replacements there).
Will this have an unwanted affect with besieged units not losing the cohesion that might have been envisioned?
Cheers, Chris