i think valve size affects what lift/dur. we need ontop of the displacement and comp of the motor,
im not to sure (would love for the seasoned boys to chime) but port lay out (be it how the porter did it or the casting shape) would also dictate if super high lift is needed, or maybe just more duration , so to keep the valve open in the meat of the flow (area under the curve, of a flowsheet)
atleast thats how i understood it on inline4 engines LOL