Section 20-2-III - PHYSICIAN ASSISTANTA. Mississippi-specific modifier M2 should be attached to the appropriate CPT code(s) when billing services rendered by the physician assistant. B. The physician assistant is reimbursed at eighty-five percent (85%) of the maximum allowable for the procedure. C. There is only one fee allowed for each CPT code. It is the decision of the physician or the physician assistant as to who will bill for a service when both have shared in the provision of the service. Incorrect billing of the service may cause a delay or improper payment by the payer. The medical doctor (MD) must be on-site on the date of service and provide additional documentation and review of services in order for physician reimbursement to be applied.20 Miss. Code. R. § 2-III