(a) Amount of reduced payment. An employer that satisfies the requirements of § 4208.4 (c)(1) or (c)(2) shall have its annual partial withdrawal liability payment for that plan year reduced in accordance with paragraph (a)(1) or (a)(2) of this section, respectively.

(1) The reduced annual payment amount for an employer that satisfies § 4208.4(c)(1) shall be determined by substituting the number of contribution base units in the plan year in which the requirements are satisfied for the number of contribution base units in the year following the partial withdrawal year in the numerator of the fraction described in section 4206(a)(2)(A) of ERISA.

(2) The reduced annual payment for an employer that satisfies § 4208.4(c)(2) shall be determined by adding the contribution base units for which the employer is obligated to contribute with respect to the reentered facility or agreement in the year in which the requirements are satisfied to the numerator of the fraction described in section 4206(a)(2)(A) of ERISA.

(b) Credit for reduction. The plan sponsor shall credit the account of an employer that satisfies the requirements of § 4208.4(c)(1) or (c)(2) with the amount of annual withdrawal liability that it paid in excess of the amount described in paragraph (a)(1) or (a)(2) of this section, as appropriate. The credit shall be applied, a revised payment schedule issued, refund made and interest added, all in accordance with § 4208.3(c)(4).