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 whether an employer is a small employer shall be made separately with respect to each employer maintaining the multiple employer plan. (D) Special rule for small employers with 25 or fewer employees In the case of a single-employer plan maintained by a small employer who has 25 or fewer employees on the first day of the plan year (as determined under paragraph (3)(I)(ii)), the additional premium otherwise determined under subparagraph (A)(iv) shall not exceed $5 multiplied by the number of participants in the plan as of the close of the preceding plan year. (E) Wage indexing of certain amounts For each plan year beginning in a calendar year after 2018, there shall be substituted for each of the first and second dollar amounts in clause (ii) of subparagraph (A) and the first, second, and third dollar amounts in clause (iii) of such subparagraph an amount equal to the greater of— (i) the product derived by multiplying each such amount by the ratio of— (I) the national average wage index (as defined in section 209(k)(1) of the Social Security Act) for the first of the 2 calendar years preceding the calendar year in which such plan year begins, to (II) the national average wage index (as so defined) for 2016