PosApp does not model the polarization of signals. This is because they are transmitted via a cable and not over air as would be the case with live signals. Only signal Amplitude and Phase is modelled.
By contrast, if an antenna were attached to the RF output port of the simulator in order to radiate the GNSS signal to a receive antenna placed a suitable distance away (taking into account free space path loss) then there would be some polarization dependant on the antenna used (generally right hand polarization).