... It uses an expression [that is not included with Civil 3D]
Well, C3D does not ship with ANY Expressions, so this shouldn't be a big surprise.
It shouldn't... but it is though... but it shouldn't. Haha
My only point in that, is that a Surface Slope Label's Directional Arrow *should* ultimately 'slope' either up, or down OOTB... A directional arrow that just points in the direction it is drawn, is just an arrow (Leader?).
I'm not asking for an Expression for each potentiality of all customers, however, some 'useful' examples, even if opposite what I may want to use, would be helpful, IMHO. That's all.