; or (ii) in the case of an individual who has average monthly earnings (as determined under subparagraph (B)) that are in excess of the level of monthly earnings established by the Commissioner to represent substantial gainful activity, the amount of the disability insurance benefit that would otherwise apply for such individual under subsection (a)(2) reduced (but not below zero) by an amount equal to 50 percent of the excess of such individual's average monthly earnings over the level of monthly earnings established by the Commissioner to represent substantial gainful activity. (B) (i) The average monthly earnings for an eligible individual shall be equal to the quotient of— (I) the total amount of wages and self-employment income for such individual in any eligible months during the 2 calendar quarters (as defined in section 213(a)(1)) that precede the most recently completed calendar quarter