Use the UdonSyncPlayer (AVPro) example prefab, go to its Audio Source gameobject, change the spatial blend from 100% 3D to 100% 2D, it does not make a difference if "Use AudioSource Volume Curve" is checked on the VRC Spatial audio source. Upload world and test, it does not make the audio 2D. If you uncheck enable spatialization, the audio will be forced to 2D and will play through the entire world.
Spatial blends work as expected on the normal Unity video player in game.