What we do in life is ever-changing and needs to be attuned to circumstance and environment. How we do it is never-changing; it is governed by our covenant with Hashem. The Korban Oleh veYored is a circumstantial korban that is attuned to the socio-economic level of the individual, it is about the person’s product and therefore it is variable. How it is brought is governed by the never-changing Brit represented by the salt – especially in the case of the Mincha.