Trying to sub-select segment of polyline that lies on edge of polysurface

I’ve noticed that sub-object select now gives you a preview of what you will select when you hold control+shift and hover over various sub-objects. In my situation, I would like to sub-object select a polyline segment that lies concurrent with the edge of a polysurface. My issue is that it seems to go to the edge of the polysurface no matter what, and I’m unable to sub-object select the line segment of the polyline.