That is a different case: for antennas we place absorbing PML boundaries at some distance, with airbox between antenna and absorbing boundary.
What I meant here is a method to make sure that all signals at the end of the line are absorbed, regardless of line impedance. This can be achieved by running the line straight into a PML wall (no distance!). One situation where this is used in simulation is "measurement" of line impedance, input impedance at the port is then equal to line impedance because there is never any reflection from the PML side.
But of course, the "normal" testcase for a line is to place ports at both ends.