EVERY nitrous oxide kit manufacturer on earth bar one uses generic solenoids that are NOT designed to operate with nitrous oxide and are NOT suitable for pulsing. These included NOS, NX, Wilson, Speedtech, NyTrex, NS and nearly every other brand you're probably aware of. The electronic controller absolutely and 100% can NOT compensate for this design flaw and actually accentuates the problem to the point of failure.
There are NOT 'plenty of specially designed flow/delivery valves' out there, there is one and it is not available for public sale just yet. Nor is there any such thing as a multistage solenoid. The nature of electric solenoids is that they are either open or closed - no half measures. Pulsing them simply opens and closes them rapidly to 'simulate' a partly opened valve.