I don’t buy that tripling the amount of extract in our 3.7liter container will result in such a small change in ultimate pressure.
1/4 the headspace and 3x the CO2 would have me ballpark 12x the pressure. which is consistish with the ~14x I suggested above. we are using slightly different numbers (yours being more specific to the non-ideal gas in question), so 12x vs 14x is not necessarily unreasonable.