TML Calibration not working with FEM

Hi guys

I have problem with TML calibration in FEM simulation.

In a 20 Ohm line simulation on er=36 substrate with 5 um gold conductors and line width of 15.88mil, MoM givers 30dB return loss while FEM can not give better than 20 dB return loss.

When I go into details, I figure out that in FEM the TML calibration is not accurate and the wave have deformation while injecting into the structure (figure below the left side of the transmission line)

while in MoM there is not such problem and the wave injection into the structure is as TML calibration promises.

I think this is the main reason for different return losses from Mom and FEM in a simple transmission line with similiar calibration.

Any advise how to resolve TML calibration problem in FEM?

Thanks