Quasielastic excitation function measurement has been carried out for the ^4He + ^232Th system at θ_lab=160^∘ with respect to the beam direction, to obtain a representation of the fusion barrier distribution. Using the present data along with previously measured barrier distribution results on ^12C, ^16O, and ^19F + ^232Th systems a systematic analysis has been carried out to investigate the role of target and/or projectile structures on fusion barrier distribution. It is observed that for

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... ^12C, and ^16O + ^232Th, reactions the couplings due to target states only are required in coupled channel fusion calculations to explain the experimental data, whereas for the ^19F+ ^232Th system along with the coupling of target states, inelastic states of ^19F are also required to explain the experimental results on fusion-barrier distribution. The width of the barrier distribution shows interesting transition behavior when plotted with respect to the target-projectile charge product for the above systems.