Flux-2D - Specifying face region of path (post-processing)

In Flux2d, when creating a path for post-processing, how do you specify in which face region results should be displayed? If the path is defined by a line which defines the border of two separate face regions, the stress results will not be the same in one material (one side of the path/line) vs. the another (other side of the path/line).  The "Region of Section" drop-down menu is greyed-out when creating the section of the path.