The next image shows a geometry where port 2 does not have custom extents while port 1 does. In this case the two ports are treated independently, as was the case when both ports had separated custom extents. The difference is that the port plane for port 2 extends over the entire domain. Here is the mesh for port 1, showing that it is limited to the custom extent region as expected.
The next image shows the mesh for port 2. Although the port mesh extends over port 1, the eigensolve proceeds as if the two lines are completely uncoupled.
Port 1 has been made invisible in this annotation to help make it clear that, in the solver, port 2 is solved independently of port 1.
Finally, consider the case in which port 2 does not have custom extents, and port 2 is defined within the custom extents of port 1. This is treated the same as the previous situation, where the eigenmode analyses for the two ports are solved independently. Here is the mesh for port 1:
The next image shows the mesh for port 2. The port mesh extends over the entire plane, because port 2 does not have custom extents.