Reed valves are nothing more than one-way valves used to limit fluid flow to one direction only. Typically, they will open when the crankcase pressure drops below ambient pressure (piston goes up) and close when above (piston comes down). The stiffer the reed is the more pressure drop required to open it and the less air delivered to the engine - and - the more limited the upper rpm. I am not sure that I totally understand your question, but that's my answer, and I'm sticking to it.