Guilin Sun
Ansys Employee
This is a different question. I strongly suggest to create a new post later, so we will maintain the convention of "one posted question and one answer", which will be helpful for other users.
To do an overlap calculation, you will need to save the monitor data on a d-card. I think this issue is not related to the SPP mode. If the two dcards have different orientations, eg, one is in XY pane and the other is in YZ plane, it will give this error.
In addition, monitor has set a number of frequency points, whereas the source is diffent , so you will not be able to do the overlap.

If you really want to calculate their overlap, please create your own script.

I tested both FDE and FDTD, using the copydcard, both work.