Your image will not show for me, can't say why.
From the Help file: Foreslope Width
For cut sections, the width of the front-of-ditch link
IF you are in a cut section it will use the Width you specify, otherwise NOT.
It is possible that your section will need to be created using other sub assemblies. However this one is most likely doing exactly what you want it to. If you study the sections and it is NOT, then time to try another assembly.