Text to speech volume is ignored

Any value given in the frontend or in the profile below is ignored and the speech is played on max volume (very loud). Any thoughts on how to overcome this?

    "sounds": {
        "system": "aplay"
    },
    "text_to_speech": {
        "nanotts": {
            "volume": "0.5"
        },
        "system": "nanotts"
    }