So, for example, you can imagine two aircraft with same total weight, however one has a lot of cargo and little fuel in the wings, the other little cargo, but a lot of fuel in the wings. Even though the total aircraft weight is the same, the loads produced on the wings will be very different due to the mass of the fuel.
As a driver, this is what I was intending to say. When looking at the suggested Mmo in rough air, the ratio of the mass in the wings compared to the payload was about all we had to consider.
A higher fuel : payload ratio, gave us that little bit more protection.