It would be very efficient to use either row of encoders after entering the Control Detail view of the V Fader 4. Using any of the top row of encoders in the detail view could behave the same as if the lower row of encoders were used.
This will avoid the need to move hands from the row of encoders above the screen to the row of encoders below the screen when the V Fader 4 is assigned to an encoder on the top row.
This may seem trivial, but it allows for more fluid, control with less wasted motion and better ergonomics.