Symbol systems approach is worldview not a theory
Metaphors (eg inside/outside) are core to the symbol systems approach, and are a worldview that provides a framework explaining the facts rather than explanations themselves (eg of interactional entities that are neither external nor internal).
The symbol systems worldview can't explain interactional entities that don't, strictly speaking, belong to the external world or to the internal mind.
Phillip E. Agre (1993).