in lieu of the deduction provided by section 164(f) (relating to deduction for one-half of self-employment taxes), there shall be allowed a deduction equal to the product of—

(A) the taxpayer’s net earnings from self-employment for the taxable year (determined without regard to this paragraph), and

(B) one-half of the sum of the rates imposed by subsections (a) and (b) of section 1401 for such year (determined without regard to the rate imposed under paragraph (2) of section 1401(b));