Vref in A4988

[dav76]

Hi all,
as part of my tuning to my I3X I also had to increase the Vref of the Z-motor-driver to 1.2V by turning the potentiometer.
I chose this value because I have read people recommending values between 0.8V and 1.2V. However, I am puzzled by the fact that this recommendation seems to apply to all three axes. Yet, the Z-axis driver is actually driving 2 motors rather than one. So shouldn't it provide twice as much current? So shouldn't Vref be increased to a range like 1.6-2.4V?

thanks

dave