If the user wants to get the input impedance in the 2 port configuration and without specifying power at port 2 I would suggest to use the following
see Eldo RF Tutorials)
.DEFWAVE Zin=50.0*{1.0 + s(1,1)} / {1.0 - s(1,1)}
.EXTRACT fsst label=Zin_r yval(wr(Zin), fund1)
rather than using Z11 (which is not the correct input impedance).
Comment:
Z11 corresponds to Zin only in a 1 port configuration. In a 2 port configuration Z11 is the input impedance only when the output is open (port 2 not connected).