low S11 parameter in HFSS

I simulated a simple rectangular waveguide in HFSS and compared with reported values of S-parameters in literature. The literature also obtained these values with HFSS. My S-12 agrees well with the literature values. My S-11 values don't agree too well. My S-11 is about -80dB. Literature shows about -40dB. Both are low values. Is this something that needs to be taken seriously?

There is no difference!!!!!
Is it important to have a VSWR = 0.0001
versus VSWR = 0.00000001? Or in other words
the transmitted power is something like 99.999%
versus 99.9999999%?.

Thanks.