The study presented in this paper focuses on a dimensional theory to augment agent nonverbal behavior including emotional facial expression and head gestures to evaluate subtle differences in fine-grained conditions in the context of emotional storytelling. The result of a user study in which participants rated perceived naturalness for seven different conditions showed significantly higher preference for the augmented facial expression whereas the head gesture model received mixed ratings: significant preference in high arousal cases (happy) but not significant in low arousal cases (sad).