Would it be better to think in terms of contact patch? Assume the average rider and bike total 200lbs, rides tyres that are 2.2″ wide on the ground at 30psi, therefore the contact patch length is ((200/30)/2.2)/2=1.5″.
Go to narrower tyres and pressure has to go up to maintain contact patch length. Increase weight and pressure has to go up. Assuming you’re on HR 2.35 or similar size tyres you’d need pressure around 44psi for an 18.5 stone rider, as you’ve found!
However, weight tends to be split 40/60 F/R so your rear tyre should be 20% harder, your front 25% softer, so instead of 30/30 you’d have 23/36.
Obviously this can be done by hand once you’ve calibrated your manual pressure meter.
In theory…