The flow/pressure ratio through a restrictor obeys the square-root law. Have a look at the chart below. A pressure span of 0-500psi for a M5 jet. A total possible flow of 700cc/min.
Interestingly, 70% (500cc/min) of the jet's total flow is delivered in the first 250psi ramp. The remainder 30% (200cc/min) is delivered in the next 250psi pressure ramp. This is confirmed by the results I posted earlier on the 0.3mm jet. A pressure change between 125 to 160psi only added another 4-5cc/min of flow on top of the 100cc/min.
