The RF3p eigenmode solver is optimized for lower-order modes, and it therefore gives best performance on port planes with only a few conductors. As the number of conductors on the port plane increases, the eigenmode solver efficiency and robustness decreases.
In this situation, you can greatly reduce your simulation runtime and memory load by defining custom wave port extents that exclude extra conductors from the port solve eigenanalysis. You can also significantly speed up your simulation by using custom extents to separate wave ports that you know do not interact on the port plane.
You should use care with these techniques. If one of the excluded conductors is relevant to the desired mode solution, using custom extents will produce the wrong mode solution. Additionally, if the custom extents are not large enough to encompass the desired mode, the resulting mode will not be a good approximation of the desired mode. If you avoid these situations, however, the custom extent wave port can greatly speed up your simulation time without sacrificing accuracy.