Hello again,
then the difference in inductance must have a real, physical background.
My best guess, with having seen your model and port setup, is that you have significant inductance in the ground return path of your model. Inductance is always for a closed loop, so the result includes both the "signal" path through the MEMS switch AND the return path from port 1 ground to port 2 ground. Closed loop!
This ground return issue is described here, starting at page 41:
**broken link removed**
Maybe you can post a screenshot of the port configuration, or send this to Sonnet support?
Best regards
Volker