Function XPLMSetAudioFadeDistance 

pub unsafe extern "C" fn XPLMSetAudioFadeDistance(
    fmod_channel: *mut FMOD_CHANNEL,
    min_fade_distance: f32,
    max_fade_distance: f32,
) -> FMOD_RESULT

XPLMSetAudioFadeDistance

Set the minimum and maximum fade distances for a given sound. This is highly unlikely to be 0 - please see https://documentation.help/FMOD-Studio-API/FMOD_Sound_Set3DMinMaxDistance.html for full details. This will set the sound to 3D if it is not already. You can set a 3D sound back to 2D by passing negative values for both min amd max.