Actually data provided in table concur. At 390lbs load patch is 60 and pressure 6.5psi 60x6.5=390, and at 774 patch 75 ant pressure 10.3, 75x10.3=773, close enough. What seemed to be an argument that pressure increases with tire load, and that tire does not behave like ideal balloon due to sidewall stiffness and initial geometry, so the relationship is not direct at boundary conditions. So patch of tire with zero load will not be zero.
Since we had measured patch and pressure for front and rear tire, we can make more accurate assumptions about tire load. The load on tire is within Liniar range of 300 to 800lbs and fig is high profile soft sidewall tire, so