(a) In applying the child support guidelines for an obligor who has a disability and who is required to pay support for a child who receives periodic benefits as a result of the obligor's disability, the court shall apply the guidelines by determining the amount of child support that would be ordered under the child support guidelines and subtracting from that total the amount of benefits or the value of the benefits paid to or for the child as a result of the obligor's disability.
(b) If a child for whom the obligor owes child support receives a lump-sum payment as a result of the obligor's disability and that payment is made to the obligee as the representative payee of the child, the credit for the lump-sum payment must be applied as provided by Section 157.009.