Double sandbar systems are common morphological features along sandy, wave-dominated, micro-to meso-tidal coastlines. In the companion paper, we demonstrated how various alongshore inner-bar rip-channel patterns can develop through morphological coupling to an alongshore-variable outer bar. The simulated coupling patterns are, however, scarcely observed in the fi eld. Instead, inner-bar rip channels more often possess remarkably smaller and more variable alongshore length scales, suggesting that coupling mechanisms do not play a substantial role in the overall double-sandbar dynamics. Here we use a numerical model to show that the relative importance of self-organization and morphological coupling changes in favour of the latter with an increase in waterdepth variability along the outer-bar crest. Furthermore, we fi nd that the typical alongshore variability in inner-bar rip-channel scale is indicative of a mixture of self-organization and morphological coupling rather than self-organization alone. Morphological coupling may thus be more important to understanding and predicting the evolution of inner-bar rip channels than previously envisaged.