I dont see how it needs to occur at all, I have a Purple Hero, who is Physical, since they can only use their own card, and that they are unable to do any magic attacks, why is +Magic Attack even an option for that leader, surprise my only card and thats what I got. You may as well have a generic hero card because thats exactly how it functions. So I would like to suggest that you either just have a generic Hero card that works on any Hero, of a particular hero, or you make the gains specific to the Hero concerned. I dont see this as too much of an issue.