VRC_SpatialAudioSource document describes limitations for custom avatar audio.
> The far radius, (snip) Avatar audio is limited to a maximum of 40m.
> "Use Spatializer Falloff" is always enabled for user voices and custom avatar audio.
I understand this limitation is for safety and comfortableness.
Then, how about "Volumetric Radius limitation" ? I think it's also need to be restricted to smaller value.
(Edit. add below)
Is it possible to add AudioSource component without VRC_SpatialAudioSource on avatar? If no, please write about that to "Whitelisted Avatar Components" (https://docs.vrchat.com/v2019.2.5/docs/whitelisted-avatar-components) and VRC_SpatialAudioSource