It is often required to annotate slope along sublayers. Typical example is to annotate the top of the subballast in track design.

The expression allows to do many things but it doesn't work as expected.
Even you specify the point names such as L_Subballast CL_Subballast and R_Subballast, it doesn't annotate because CL_Subballast is not on Top.

The only way to get it annotated is to create a second corridor ensuring features are on top. That is really painful.

At least, I want to be able to annotate all segments created explicitly using point names.