I don't see the problem with the rules as they have been confirmed. If a stack of units having the same modifier suffers a KIA result, they are all affected by that result. If they have different modifiers, they undergo their own attacks albeit using the same DR. The suggestion that, in effect, they should suffer two attacks when the attacker gets a lucky KIA roll seems to me to be excessive. At the end of the day, it is a game and speculating about how DR results might translate to real life is a futile exercise. They are an abstraction as opposed to an attempt to mimic reality (whatever that reality might be).