In general
In the case of any partial disposition for which an election under this subsection is made, the increase in basis under paragraph (1) shall be an amount—
(i)#
which bears the same ratio to the increase which would be determined under paragraph (1) (without regard to this paragraph) with respect to the entire interest, as
(ii)#
the amount of the tax imposed under section 2032A(c)(1) with respect to such disposition bears to the adjusted tax difference attributable to the entire interest (as determined under section 2032A(c)(2)(B)).