Update details (ver.5):
Added Tracker1 to Tracker8 to the "Choose Target" selection as suggested by
@Origin69. This can actually be selected by people who don't have Tracker.
Use Tracker selection in VR mode. If you don't have Tracker, you can choose any number. If you have a tracker, I think an unused number is good, but I don't have a tracker, so I can't confirm if it works properly with a tracker. Please let me know if you have any problems.
The difference in behavior between when CenterEye is selected and when Tracker is selected is
CenterEye : Atom always moves in front of the player's line of sight when the player's head is moved.
Tracker: Atom does not move when the player moves his or her head, and is always in a fixed position relative to the player's virtual body. I think that the behavior is similar to when using this plugin in desktop mode.
In any case, if the player moves or rotates with the controller, Atom will follow.