Except as otherwise provided in this part, the covered health benefits provided to subscribers shall be equivalent to those provided to state employees through the Public Employees’ Retirement System for the most recent plan year preceding the applicable program plan year, except that the plans may provide a mechanism for inpatient hospital care provided under the mental health benefit through which applicants may agree to a treatment plan in which each inpatient day may be substituted for two residential treatment days or three day treatment program days.