How much oil pressure should the head have at idle and at 3000-4000rpm?

The tech manual I have said the motor should have at least 50psi@3000rpm. When I check the oil pressure at the oil pressure sensor on the block it make good oil pressure (80psi@3000). My problem is when I check the oil pressure on the head it is at 30 - 40psi@3000, which isn't enought to activate vtec. Any suggestion on what my problem can be.