For the engine settings, we use the default settings, except for "Thread Factor". The "Thread Factor" setting essentially tells the FDTD engine how many CPU threads to use during the time-marching loop.
For a given system, some experimentation may be needed to determine the best number of threads to use. In many cases, using half of the available hardware concurrency works well. This comes as a result of there often being two cores per memory port on many modern processors. In other words, for many problems, the FDTD solver cannot load and store data from CPU memory quickly enough to use all available threads or hardware concurrency. The extra threads are idling waiting for data, and a performance hit is incurred since due to increased thread context switching takes some time.
Also,