Stacked frequency polygons share almost all of normal Frequency Polygon's properties.
The Join Polygon to x-Axis option is not present because it does not make sense for Stacked Frequency Polygons.
Stacked frequency polygons only differ from normal frequency polygons in how they handle multiple data sets. Normal frequency polygons overlay the polygons. Stacked frequency polygons stack the individual data sets on top of each other. Exactly the same data is present.
Normal Stacked