The yield on investments is materially higher than the yield on the issue to which the investments are allocated if the yield on the investments over the term of the issue exceeds the yield on the issue by an amount in excess of the applicable definition of MATERIALLY HIGHER set forth in paragraph (d)(2) of this section. If yield restricted investments in the same class are subject to different definitions of MATERIALLY HIGHER, the applicable definition of MATERIALLY HIGHER that produces the lowest permitted yield applies to all the investments in the class. The yield on the issue is determined under section 1.148-4. The yield on investments is determined under section 1.148-5.