Question Where is the origin of the Center Eye for the Tracked Pose Driver?

I'm developing a multiplayer game, and I need to match a player model's head position with their camera position appropriately. The camera (in XR Rig) has a Tracked Pose Driver component whose Pose Source is set to "Center Eye - HMD Reference." Where would this correspond to exactly on a model? Right in between the eyes (if so, in the middle of the eyeball or on the front or the back)? In the middle of the head? In the middle of the physical device (head-mounted display)? I'm currently using an Oculus Quest.