If no Federal payment is due, compute the excess income. The excess income in the
                        payment computation is the difference between the BM's CI and the CM FBR (plus any
                        essential person increment). If the Federal payment limit for FLA D was used in the
                        Federal payment computation, the excess income is the difference between the BM's
                        CI and the FLA D payment limit.
                     
                     If there is no excess income in the payment computation (whether or not there is excess
                        income in the CM), the full OSS payment level is payable.
                     
                     If there is excess income in the payment computation, it is subtracted from the CM
                        OSS payment level; the remainder is the OSS payment.
                     
                     If the excess income in the payment computation equals or exceeds the CM's OSS payment
                        level, no OSS is due.