Site flatten - top down
I am attempting to show/create an excavated hole in the ground. The existing ground surface is in the 500-530' elev range the hole will be dug to a depth of 400' elev. The excavation boundary at the surface is constrained to a defined boundary. Therefore, the excavation needs to be inside this line. Wall slope is 70 degrees.
I draw the area to represent the limits of excavation at the surface, select that area, then do the Calculate Flattened Site Plan Grid option. The resultant grid surface is drawn such that GM apparently sets the boundary area at 400' and works it way back up (bottom up). I need it to work top down as shown by the green line in the screenshot.
I've tried the various options and none will seem to do what I want. Any recommendations?