Hello Hector,
sorry for the late reply - we had some issues with the system that was down for a couple of days.
The height in the model is defined as the "mean" height, so I would assume anything between the two figures you have in your drawing.
You know the layered model in WEST (Takacs) may be more detailed than a point, or ideal settler, but still ideal (or an approximation) in terms of the geometrical description of the tank.