If you have a damage/heal volume set to lava/acid and are in third-person, the post-processing effects apply when your camera is close to the volume, not when your player is close to the volume.
Steps to Reproduce
Enter third-person and go next to a lava/acid damage/heal volume.
What I expected to happen
The overlay appears when your player is close to the volume.
What happened
The overlay doesn’t appear when your player is close to the volume, only when your camera is close to the volume.