What about the make of the tire? I mean don't you think that depending on the structure of each tire, the "sweet" spot can change?

large and buffy shoulders tend to wear on the outsides with low pressure, so going higher can help in achieving even wear...

I am having 30 all around the Vredesteins, and when i tried to see how they are wearing, I noticed that it is even, with some more from the center. now ask me how did i noticed this with only 500 miles? :D well, there is this transversal rubber line where the molding was done... I noticed that it disapeared completely from the center, with some very light traces on the outsides... So inflating more will cause the center to wear faster than the sides, so I concluded that the footprint on the tire seems balanced and optimized (and the handling seems nice as well) maybe because the Vs shoulders are slim... and since winter is around the corner, I decided to leave them 30 all around at cold.

You are a very wise person. :D