An arrangement is described for fitting a hearing prosthesis system to a prosthesis patient. The PAMR measurement determines a post-auricular muscle reflex (PAMR) response of the patient to an auditory stimulus signal. For example, the PAMR response may include a PAMR amplitude growth function or a PAMR threshold stimulus level at which a PAMR is measured in the patient. Then a patient fitting module sets an operating characteristic of the hearing prosthesis system based on the PAMR response.