Problem:
A zone not behaving as intended, not following the reverse slope (against the main slope).  Using the green subzone to push the slope to the eastern direction while the main slope is defined going to the western direction.

Solution:
The minimum slope defined is wrong.  If the goal is to reverse the grade to the main slope, use negative numbers BUT it should be defined as the maximum.

It should be defined as the MAXIMUM while still adding a figure in the minimum to overwrite the settings in the boundary zone.  The minimum is set to -2.0 and the maximum is set to -0.1 (desired figure).  The reason for this set-up: a large negative number (i.e. -2.0) is actually smaller than a smaller negative number (i.e. -0.1).  A good analogy: when you have -$2, you actually have less money than if you have -$1.

Recalculate: