> When port impedance and line impedance match.
This sentence makes no sense. Maybe your text is mis-formatted?
I am curious: The differences seem marginal (on S11 levels of ~-70 dB). What kind of a circuit do you have where this is relevant?
Maybe its an effect of higher order modes in the microstrip: https://www.microwaves101.com/encyclopedias/microstrip
I think they should not be present with your freq/substrate spec, but maybe the onset of them is visible on these tiny power levels. And maybe the software packages use different models that include these modes or not.
You could 3DEM-model it. Check the EM simulation examples on the qucsstudio website.