If the calculated pressure exceeds your tire’s rated maximum, choose a wider tire. If the calculated pressure is below your tire’s safe minimum, choose a narrower tire.

Derived from Optimizing Your Tire Pressure for Your Weight by Jan Heine; or a more extensive version, “PSI RX” by Jan Heine, Adventure Cyclist magazine, March 2009. Heine’s chart is a set of straight lines: I simply measured them to work out their parameters.

This archive argues that the whole 15% drop premise is flawed.