It isn't a problem of how far the lever moves, but how much cable per click. If you use an '80s Syncro 7 speed shifter to shift an 8 speed geometry derailleur, you would only shift across 5 gears before you had used all 7 clicks. That's "pull ratio". We are thinking that this old Euclid has a 1.43 pull ratio, but a 7 speed Syncro shifter is built for around 2.0 ratio.