CST MWS： S21 doesn't change despite separation distance

Hello all,
I am trying to determine the power read at the receiving waveguide port due to the reflected power off the PEC wall from the transmitting waveguide port.
The setup is 2 waveguides, stimulated with waveguide ports, slightly separated from each other and both facing a finite PEC wall in free space at a fixed separation distance.
When I change the distance between the waveguide to PEC wall I notice that the S21 does not change at all.
I attached the model in a zip if anyone is interested. What am I doing incorrectly? I can upload results too if needed.
Thank you for your time,
otterboi

SOVLED. Needed to use time gating to correctly read the reflected energy.