In the case of any mortgage insured under any provision of this subchapter that is executed in connection with the construction, rehabilitation, purchase, or refinancing of a multifamily housing project for which equity provided through any low-income housing tax credit pursuant to section
42 of title
26, if the Secretary determines at the time of issuance of the firm commitment for insurance that the ratio of the loan proceeds to the actual cost of the project is less than 80 percent, subsection (a) of this section shall not apply.