I suggest that the concept of proportionating the appropriate inflation pressure from max. load and max. inflation pressure is unlikely to hold good when tires are of a different build. The ideal inflation pressure arises from a large number of factors, such as spring rate, damping, and steering geometry, as well as weight, and will vary according to the physical characteristics dictated by the carcass design. Those characteristics involve max. load and pressure, but a great deal more.
When manufacturers develop a new model, they choose a tire and experiment to arrive at their sticker value. That ideal value is not going to hold for a tire with different build characteristics, even when adjusted for the above tire data. You need to experiment up and down from the sticker value, bearing in mind that higher values use less fuel, but reduce adhesion, and ideal inflation will result in even wear across the tread. As always, engineering is a compromise.
