(1) Payment for hospital residents will be made as follows:

(a) upon obtaining hospital residency status, claims for that recipient may be billed on an interim basis;

(b) payment for the first 180 days of inpatient care will be the DRG payment for the case as computed in ARM 37.86.2907 and any appropriate outlier payment as computed in ARM 37.86.2916; and

(c) payment for all patient care subsequent to 180 days will be reimbursed at a rate computed by multiplying the statewide average cost to charge ratio by the usual and customary billed charges.