Surround : Surround Panning and Mixing : Surround Panner Controls : Position Controls

Position Controls
The Position controls let you set the positions of the panner.
 
Front
Displays and controls the current front X-axis (left/right) position of the panner.
Rear
Displays and controls the current rear X-axis (left/right) position of the panner. In default X/Y Panning mode, Rear is linked to Front position and cannot be controlled independently.
F/R (Front/Rear)
Displays and controls the current Y-axis position of the panner.