 Slow-roll amplitude of the squeezed zeta zeta-prime-squared bispectrum

The undifferentiated soft-leg permutation gives $B(q,k,k)\simeq (ϵ/2)P(q)P(k)$ as $q/k\to 0$. It retains a squeezed $q^{-3}$ enhancement, but corresponds to local amplitude $f_{\mathrm{NL}}^{\mathrm{effective}}=5ϵ/24$. Soft momentum placed only at derivative slots would miss this dominant term.