; and (v) in any other case, the amount determined under paragraph (3)(A)(i). (B) Small employer premium phase-out (i) In general In the case of a single-employer plan maintained by an employer who has more than 500 employees but not more than 600 employees on the first day of the plan year, the annual premium rate payable to the corporation by such plan for basic benefits guaranteed under this title is an amount for each individual who is a participant in such plan during the plan year equal to the sum of— (I) the annual premium rate that would be so payable by such plan if such plan were maintained by a small employer for such plan year, plus— (II) the applicable percentage of the excess of— (aa) the annual premium rate so payable by such plan without regard to this subparagraph, over (bb) the annual premium rate that would be so payable by such plan as described under subclause (I). (ii) Applicable percentage For purposes of this subparagraph, the applicable percentage is the ratio (expressed as a percentage) of— (I) the number of employees of the employer to the extent such number exceeds 500, over (II) 100. (C) Special rule for multiple employer plans In the case of a multiple employer plan (other than a CSEC plan (as defined in section 210(f))), the annual premium rate payable to the corporation by such plan for basic benefits guaranteed under this title is the sum of the annual premiums that, if each employer maintaining such plan were treated as maintaining a separate plan in which— (i) the number of participants equals the number of participants in the multiple employer plan who are employed (or formerly employed) by such employer, and (ii) the amount of unfunded vested benefits equals the portion of the unfunded vested benefits under the multiple employer plan attributable to such employer, would be imposed on each separate plan in accordance with this section. In determining the annual premiums that would be imposed on each of the separate plans described under this subparagraph, the determination of