Only effective with the box positioned within the AC.
Box base thickness and AC to KC passage height and groove profile depth divergence.
A descending object engaged with the profiled runners would be deflected from the south wall by an amount equal to the maximum depth of the profile runners. The greater degree of deflection beginning at (yellow/green) juncture.
A descending object at the lower end of its stroke, (lower blue), and deflected by the profiled runners would contact the internal floor of the box at the point of maximum deflection. (lower blue)
Correlations such as these only become apparent through drawing construction.
The act of drawing forces and enables observation.