This quote from an article explains it much better than I can, maybe the difference is the way the inductor extends into the magnets as you mentioned. I have also heard that there is a very slight difference in the taper of the inductors between the V and Z.
"The Magforce V system uses centrigual force developed by the spool to move the inductor into the magnets. Braking action does not occur on startup until sufficient centrigual force develops (with spool speed) to overcome spring tension and then the inductor begins to move further into the magnets. As spool speed continues to increase, the inductor is fully inserted into the magnets and maximum braking occurs, until spool speed is eventully reduced and the inductor begins to move back out of the magnets (applying less braking).
Magforce Z is very similiar to Magfoce V, except the point that braking starts to occur is at a higher spool speed, and maximum braking occurs at a higher spool speed as well. Braking is also reduced at a higher spool speed . So, you can think of Magforce Z as a higher speed Magforce V braking system -- only really applying most braking action at the highest spool speeds. The net effect is that overall efficiency of braking action is improved and the spool will spin-up faster and theoretically achieve higher average spool speeds for a longer period of time. In addition, Magfoce Z is theoretically quicker to respond to rapid changes in spool speed during the cast (like the slight increase in spool speed due to the lure being affected by a blast of wind).
In reality, most anglers don't notice much difference between Magforce V and Z except when casting lighter lures into/across the wind. [Most of the braking action between the two is the same with heavy lures, since the spool spins up so quickly and maximum braking is so rapidly applied in both systems.] However, with a light lure, Magforce Z is quicker to resond to small changes in spool speeds, and therefore can apply more incremental braking action when the spool speeds up due to the effect of wind on the line."