Stereo sources are virtual sources. They are composed of two mono sources.
The position of a stereo object is set by its center and its Stereo Width. The center of the source can be moved in the 3D Venue (similarly to mono sources), or positioned by entering its coordinates in the 3D Parameters section of the inspector.
Other 3D parameters are similar to mono sources 3D Parameters.
The Stereo Width sets the total spreading angle of the left and right channels around the center. For example, the default 30° width sets the left channel at -15° and the right channel at +15° around the center displayed in the 3D Venue.