The capture-fission cross section for the S36+Pb208 reaction was measured for seven center-of-mass energies ranging from 147.5 to 210.2 MeV. A comparison of the deduced interaction barriers from "distribution of barriers" measurements and simple 1/Ec.m. plots for 13 well-characterized systems shows the validity of the latter approach for deducing interaction barriers, especially for reaction systems involving radioactive beams where the former measurements are not currently feasible. Application of the 1/E c.m. plot technique for the S36+Pb208 reaction gives an interaction barrier height of 140.4±1.4 MeV. This value as well as the deduced interaction barriers for all known studies of capture cross sections with radioactive beams are in good agreement with recent predictions of an improved isospin-dependent quantum molecular dynamics model and a modified version of capture cross-section systematics by Swiatecki The deduced barriers for these n-rich systems are lower than one would expect from semiempirical systematics based upon the Bass potential. In addition to the barrier lowering, there is an enhanced subbarrier cross section in these n-rich systems not predicted by the Bass potential systematics. These enhanced subbarrier cross sections may be important in the synthesis of the heaviest nuclei.