You are arguing a straw man though, nobody is talking about standardization, we are talking about transparency. If you as a manager can justify the difference

You are arguing a straw man though, nobody is talking about standardization, we are talking about transparency. If you as a manager can justify the difference then having the salary transparent shouldn't be a problem. If you can't, then there's a problem. If you are the one receiving the salary, I don't see why you should have to defend yourself anymore than we have people"defending themselves" for living in a nice neighborhood. It simply doesn't come up. Just point to the manager/employer and say "ask them"