At Shacharit, a right handed Ashkenazi (RHA) wearing tefillin on their left arm puts their head on the right arm. At Mincha, RHAs put our heads on the left arm.
At Shacharit, what should an RHA not wearing tefillin do? Right arm, like everyone else at the time, or left, like is done when not wearing tefillin later?
(Examples of people who wouldn't be wearing tefillin: someone under bar-mitzvah, or who doesn't have tefillin accessible, or is unable to keep themselves 'clean', or are lazy.)