How to control multiple audio selectors volume in a single video input in Media Convert

I have been trying to control the volume of 3 different audio selectors in a video input without success. The idea is:

1. Mute the sound of the first audio selector (the one reflecting the audio of my video input)
2. Keeping the sound of the second audio selector at its original level. This audio selector uses an external file in which I have a narrator track. It is also my checked as my "default" audio.
3. Reducing the sound of the third audio selectors which is used as a background music

To achieve all this, I have played around with the "channel mapping" from the "Input remix controls" in order to assign DB levels in every inputs/outputs channels. All my attempts were unsuccessful. It seems that as soon as I use the "Input remix controls" in any audio selectors, only my first audio selector is being outputted in my transcoded file.

Maybe there is something I don't understand but, I was under the impression that it would be feasible for every audio selector to control the sound level.

Here is an example of by job JSON:

{
  "Settings": {
    "TimecodeConfig": {
      "Source": "ZEROBASED"
    },
    "OutputGroups": [
      {
        "Name": "File Group",
        "Outputs": [
          {
            "ContainerSettings": {
              "Container": "MP4",
              "Mp4Settings": {}
            },
            "VideoDescription": {
              "CodecSettings": {
                "Codec": "H_264",
                "H264Settings": {
                  "MaxBitrate": 2500000,
                  "RateControlMode": "QVBR",
                  "SceneChangeDetect": "TRANSITION_DETECTION"
                }
              }
            },
            "AudioDescriptions": [
              {
                "AudioSourceName": "Audio Selector Group 1",
                "CodecSettings": {
                  "Codec": "AAC",
                  "AacSettings": {
                    "Bitrate": 128000,
                    "CodingMode": "CODING_MODE_2_0",
                    "SampleRate": 48000
                  }
                }
              }
            ]
          }
        ],
        "OutputGroupSettings": {
          "Type": "FILE_GROUP_SETTINGS",
          "FileGroupSettings": {
            "Destination": "aaa/bbb/ccc/"
          }
        }
      }
    ],
    "Inputs": [
      {
        "AudioSelectors": {
          "Audio Selector 1": {
            "DefaultSelection": "DEFAULT",
            "AudioDurationCorrection": "AUTO",
            "RemixSettings": {
              "ChannelMapping": {
                "OutputChannels": [
                  {
                    "InputChannelsFineTune": [
                      -60,
                      -60
                    ]
                  },
                  {
                    "InputChannelsFineTune": [
                      -60,
                      -60
                    ]
                  }
                ]
              },
              "ChannelsIn": 2,
              "ChannelsOut": 2
            }
          },
          "Audio Selector 2": {
            "ExternalAudioFileInput": "narrator-video.mp4",
            "Offset": 0,
            "AudioDurationCorrection": "AUTO",
            "RemixSettings": {
              "ChannelMapping": {
                "OutputChannels": [
                  {
                    "InputChannelsFineTune": [
                      0,
                      0
                    ]
                  },
                  {
                    "InputChannelsFineTune": [
                      0,
                      0
                    ]
                  }
                ]
              },
              "ChannelsIn": 2,
              "ChannelsOut": 2
            }
          },
          "Audio Selector 3": {
            "ExternalAudioFileInput": "bg-video.mp4",
            "Offset": 0,
            "AudioDurationCorrection": "AUTO",
            "RemixSettings": {
              "ChannelMapping": {
                "OutputChannels": [
                  {
                    "InputChannelsFineTune": [
                      -30,
                      -30
                    ]
                  },
                  {
                    "InputChannelsFineTune": [
                      -30,
                      -30
                    ]
                  }
                ]
              },
              "ChannelsIn": 2,
              "ChannelsOut": 2
            }
          }
        },
        "VideoSelector": {},
        "TimecodeSource": "ZEROBASED",
        "FileInput": "main-video-footage.mp4",
        "InputClippings": [
          {
            "StartTimecode": "00:00:00:00",
            "EndTimecode": "00:00:35:23"
          }
        ],
        "AudioSelectorGroups": {
          "Audio Selector Group 1": {
            "AudioSelectorNames": [
              "Audio Selector 1",
              "Audio Selector 2",
              "Audio Selector 3"
            ]
          }
        }
      }
    ],
    "FollowSource": 1
  },
  "AccelerationSettings": {
    "Mode": "DISABLED"
  },
  "StatusUpdateInterval": "SECONDS_60",
  "Priority": 0,
  "HopDestinations": [],
  "Role": "arn:aws:iam:xxxxxxxx"
}