I might be wrong, but you're not resetting the snrValues and rssiValues between runs, so they keep accumulating, so the "actual" run is actually averaging the results from the previous runs.
If I'm right, then you should see only the first values in your output file changing.
I have used wifi-vht-network.cc and adds some custom functionality with one Server apart from Ap and wifinode. So I am using p2p link from Server to AP with 1Gbps and 10microseconds delay. Use TCP downlink traffic from server to wifinode. Use FrissPropogationModel/LogDistancePropogationMode, IdealWifiManager, AP and wifinode with fixed distance of 10m and set up Parabolic antenna at AP and omnidirectional at wifinode now calculating for different orientations of parabolic antenna how RSSI change at wifinode to follow radiation pattern but I am getting same RSSI for every orientations.I have used MonitorSnifferRx and callback function but still didn't get anything. I am unable to detect the exactly where I am doing wrong. Also tried every other approach for debugging but still showing same results. I am attaching the .cc file. Please let me know if somebody can troubleshoot this issue.