Forcing HFSS to ignore a certain region

I want to force HFSS to not mesh a particular region in a model. The model that I have includes a multilayer circuit board that is not very relevant to the region that I want to simulate. It is acceptable to me if the entire multilayer circuit board is modeled as a block of PEC, which is exactly what I did. I created a box of PEC enclosing the region I am not interested in. However, when I plot the mesh, the region that I placed the PEC box in is still meshed

If I plot Mag_E along a line that passes through the box, the points that coincide with the PEC box are not plotted, which indicate to me that the solution indeed is consistent with the PEC box being there, but when I plot the mesh on a plane that cuts the box, I see triangles there.

Material override is enabled.

Is the PEC really meshed, or what am I supposed to do?