TrueVolume Metal Model
The TrueVolume model divides the volume of a thick conductor into rectangular metal cubes, and then uses Sonnet's volume subsections to model those cubes. These volume subsections account for the full 3D geometry of a subsection in all coupling calculations. Therefore, the physical thickness of the metal conductor is inherently accounted for with the use of volume subsections.
For a detailed discussion of TrueVolume metal, please refer to TrueVolume in the Sonnet User's Guide.