Custom voice is not passed from Assist to Piper addon request

So I uploaded the custom voice files to /share/piper and it’s recognized by Home assistant

I’m certain the custom voice is working as I can manually call tts.speak service and the GLaDOS voice comes out from the speaker. And the Piper addon log shows that GLaDOS voice is being picked.

action: tts.speak
target:
  entity_id: tts.piper
data:
  media_player_entity_id: media_player.home_assistant_voice_09f684_media_player
  message: That thing you burned up isn't important to me; it's the fluid catalytic cracking unit.
  options:
    voice: en_US-glados-medium


However, when having conversation with the assist, the voice argument is missing in the request, thus the default voice is used to generate voice.

May I ask if it’s a known problem and how to fix that? Thanks!