Hi,

Physics can't be purported, it is either about right or nonsense.

Compare two tyres at the same pressure say but one is twice
the width, thus it contains 4 times as much air as the other.

Simplistically you can model the fat tyre as a quad of the
thin tyre glued together. Consider a load than compresses
the fat tyre 15% - treating it as 4 thin tyres each one is
compressed 15% but is only bearing half the load.

Its clear the thin tyre at this pressure is grossly underinfated
for the load and would compress ~ 30% to support the load.

Conversely consider a pressure for the thin tyre that gives
15% defection. Arranged as quad with the same load each
one would only deflect ~ 7.5%, its clearly grossly overinflated.

If 15% is ideal, your clearly giving up lots of comfort and grip,
for an advantage only apparent on very smooth surfaces.

Tests of rolling resistances and power often don't include
the rider in the equation. Apparently the extra harshness
passed to the rider to be absorbed by the rider makes
the bike feel faster, when it isn't, and more tiring, so
the extra pressure is really slowing you down overall.
(And wearing your bike out at a faster rate.)

65-70psi is appropriate for 28mm to 32mm tyres if
a "tiredrop" of 15% is taken as "ideal". YMMV and
prefer a less or more number as right for you.

rgds, sreten.