Calibration for Edge ports and sources?

[fnightdeference]

Sim4Life Light

When simulating a microstrip transmission line, which I know to be a very good match based on measured results and simulation, my return loss remains quite poor. The documentation does not tell me much about how to perform padding of the ABS boundary, nor if there is de-embedding / port calibration for the edge sources.
Line:
w=0.58mm
l = 20 to 40mm
substrate:
er=3.55
h = 0.254mm
Edge source
Meshing grid or termination settings don't affect the results, so I assume that the meshing is fine enough.
Is there any more information available on the edge source when exciting microstrip?

I have gone through the Tutorials, but these don't give much guidance either - for the most part 20dB return loss is often good enough, but I'm trying to optimise to >30dB return loss.