We recently showed that two systems have the same nonlinear flow dynamics if they have (1) the same number of entanglements, Z, (2) the same number of Kuhn segments between entanglements, N-e, and (3) a single monomeric friction reduction between all species. Because differences in polymer chemistry result in different values of (1)-(3), these results show that the likelihood of two melts having the same nonlinear behavior is improbable. This work determines the dependence of the nonlinear extensional flow behavior on N-e for three polymer melts: polystyrene, poly(methyl methacrylate), and poly(tert-butylstyrene). We show that polymer melts with the same Z have almost identical scaled linear viscoelasticity. Extensional rheology at constant strain rate shows strain hardening depends strongly on the value of N-e. More specifically, our data suggest a power-law dependence of steady state stress on the Weissenberg number which increases with increasing N-e.