The role of rainbow scattering in enhanced ion scattering near 180\ifmmode^\circ\else\textdegree\fi{} was explored by comparing calculated enhancements for protons and antiprotons. Since the rainbow effect does not occur for negative particles and since the enhancement was much smaller for them than for positive particles, this comparison demonstrated in a more direct way than previously done the importance of rainbow scattering in producing the enhancement. A procedure for calculating a similarity factor between the ingoing and outgoing portions of a trajectory was developed, and its use showed that trajectories returning near 180\ifmmode^\circ\else\textdegree\fi{} differ in nature from random-return trajectories. A discussion is given of the possible relationship of the enhancement to phenomena such as the correlation effect in self-diffusion by the vacancy mechanism in solids and surface-structure studies by impact-collision ion-scattering spectrometry.