Conic Slope in cut

Hi All,

I'm trying to use the Conic Slope function at the bottom of a retaining wall that is below existing ground. I can't seem to get the function to work in a cut scenario, it works fine when I force it above the existing surface (making it a fill slope). 

I've tried changing the slopes to a negative value but this does not help. I'm using OpenRoads 10.08.01.33

Any help would be appreciated.

Thanks