Other AR Face: stop tilting face prefab?

I am using ARFace Manager to get ARKit face data and map it to a prefab with blend shapes. My project differs from a typical AR project though in that I am *not* adding content to the video feed but just mapping the facial motion data onto a 3D object in the scene.

The facial motion capture works well BUT something is tilting the entire ARFaceManager.prefab object when I tilt my face. The prefab is an entire character so this tilts the character from the feet. Is there a way to disable this?

In ARKitFaceSubsystem.cs, FaceSubsystemParams.supportsFacePose seems like what I'm looking for but setting it to false has no effect.