Pretty much answered your own question there. The short-axle versions probably have the driver socket cut a bit deeper into the cup so that the crank boss doesn't crash into the cup, and I'm guessing the actual cartridge assembly is also narrower for those versions.
Pretty much answered your own question there. The short-axle versions probably have the driver socket cut a bit deeper into the cup so that the crank boss doesn't crash into the cup, and I'm guessing the actual cartridge assembly is also narrower for those versions.