Probably the bypass pressure goes up with running pressure. Might give more info on the pump.
Only reason the bypass pressure would go up is of the oil pump is pumping so much oil that the bypass cannot dump the excess.
90 psi cold is too much, 70 psi warm is too much, imo. I like to see no more than 60 psi warm cruising.
15 psi at hot idle is fine.
20w50 is way too thick. I like to use just enough oil viscosity to get the pressure I want, any more is wasting HP. Typically I run 5w30. Which also cuts down on cold oil pressure.
