HFSS - ridge waveguide modes

I would like to create the Gamma vs frequency graph of a ridge (circular) waveguide to see the cut-off frequencies of the first 5 modes. I don't know how to define the integration line, but from my first trials I obtain some results simulating ports-only. However the results of Gamma from the first port are different from those of the second port, why? What are the correct results?

I solved the problem: the mesh on the two ports was different and so I had two different solutions.