You should see the upstream bitrate change according to which bitrate is set on the downstream.
This is done with what we call "Bandwidth Adaptation". This works by default where the remote side estimates its bandwidth. It regularly reports
this value to the sender. If its downstream bandwidth is lower than the bitrate that the sender is producing, then the sender will lower its bitrate
to match and avoid overloading the receiver's downstream bandwidth and causing packet loss.
Note that bitrate increases may take longer for their
effect to be observed as WebRTC gradually increases bitrate.