The reduction under paragraph (1) for any taxable year shall not exceed an amount which bears the same ratio to the increase in the investments in export trade assets (as defined in section 971(c)) of such corporation for such year as the export trade income which constitutes foreign base company income of such corporation for such year bears to the entire export trade income of such corporation for such year.
For purposes of this section, the amount taken into account with respect to any export trade asset shall be its adjusted basis, reduced by any liability to which the asset is subject.
A United States shareholder of an export trade corporation may, under regulations prescribed by the Secretary, make the determinations under paragraphs (2) and (3) as of the close of the 75th day after the close of the years referred to in such paragraphs in lieu of on the last day of such years. A United States shareholder of an export trade corporation may, under regulations prescribed by the Secretary, make the determinations under paragraphs (2) and (3) with respect to export trade assets described in section 971(c)(3) as of the close of the years following the years referred to in such paragraphs, or as of the close of such longer period of time as such regulations may permit, in lieu of on the last day of such years and in lieu of on the day prescribed in the preceding sentence. Any election under this paragraph made with respect to any taxable year shall apply to such year and to all succeeding taxable years unless the Secretary consents to the revocation of such election.