We measured the capture-fission excitation functions for the 32S+181Ta reaction and the 38S+181Ta reaction. (The radioactive 38S beam was produced by projectile fragmentation.) In the 32S-induced reaction, an incomplete fusion component was observed at high energies, with an average linear momentum transfer corresponding to the escape of an α particle. The deduced interaction barrier heights were 130.7+/-0.3 and 124.8+/-0.3 MeV for the 32S- and 38S-induced reactions, respectively. No differences between the two reactions were observed beyond a simple shift in the interaction barrier height.