The Studio surround mixer is optimized for dialog (sometimes referred to as "Cinema'" mode). In this mode the center channel takes priority over the front left and right channels, ensuring that dialog is clearly audible in the center at all times.
The following is a brief overview of how the left and right audio channels are combined, and or adjusted depending on how the panning sliders are adjusted (Within Studio).
When a stereo clip is panned to dead center, the left and right channels are combined and sent to the center speaker. Both the left and right channels are also sent to the left and right speakers, but at half the power of what is being sent to the center.
As the clip is panned towards the front, the audio level sent to the rear speakers is decreased, as it is panned to the rear the audio level sent to the center speaker is decreased.
As the clip is panned to the left or right of center, audio is sent to the front right and front left speakers as appropriate.
A mono clip is panned in the same manner; with a mono clip panned dead center sent to the center, right rear and left rear speakers.