Except for guarantees of qualified mortgage loans and qualified student loans, a guarantee of payments on a purpose investment is a qualified guarantee of the issue if all payments on the purpose investment reasonably coincide with payments on the related bonds and the payments on the purpose investment are unconditionally payable no more than 6 months before the corresponding interest payment and 12 months before the corresponding principal payments on the bonds. This paragraph (f)(5) only applies if, in addition to satisfying the other requirements of this paragraph (f), the guarantee is, in substance, a guarantee of the bonds allocable to that purpose investment and to no other bonds except for bonds that are equally and ratably secured by purpose investments of the same conduit borrower.