High bandwidth even with strong constraints activated

In an effort to reduce the bandwidth, we tried very drastic constraint, like fixing the resolution to 180 and framerate to 10 in the config. But even after that, the bandwidth used is quite high. Each new person keeps addding about 500kbits, while with zoom we had a meeting with 10 persons and the total bandwidth stayed around 600.

This is a meeting with 4 persons, looking at chrome://webrtc-internals, the results are quite surprising:

resolution 320*180
framerate 10
bitrate 500

resolution 240*180
framerate 25
bitrate 500

resolution 321*180
framerate 10
bitrate 500

resolution 1047*740 (this person was screensharing)
framerate 5
bitrate 100

The result are quite confusing to me. Everybody had slight different resolution, and one of the person had a very high framerate, around 25, much higher that the 10 requested. And for everyone, the bandwidth seems really high for such tiny resolution.
Our config:

// Sets the preferred resolution (height) for local video. Defaults to 720.
    resolution: 180,
    startBitrate: "128",

    // w3c spec-compliant video constraints to use for video capture. Currently
    // used by browsers that return true from lib-jitsi-meet's
    // util#browser#usesNewGumFlow. The constraints are independent from
    // this config's resolution value. Defaults to requesting an ideal
    // resolution of 720p.
    constraints: {
        video: {
            aspectRatio: 16 / 9,
            frameRate: {
                 max: 10,
            },
            height: {
                ideal: 180,
                max: 180,
                min: 180
            }
        }

Is there any way to cap the bandwidth used ?