For some reason both OS and Enya plugs are an inbetween length. The extra length of a normal "long" plug makes very little difference to the compression but does put the coil slightly closer to the piston. This can have a slight affect on the ignition point but it's probably not noticeable. There's an optimum ratio (which I can't remember now) between the bore size and the distance of the plug away from the piston at TDC that's about 5:1.