Initial conditions for different CH geometries. Panel a shows an incoming wave that consists of a purely enhanced pulse (red) and a circular CH. Panel b again shows a circular CH, but with an incoming wave that combines an enhanced pulse (red) with a depletion region at the rear of the wave (blue). Panels c–f show incoming waves with enhanced as well as depleted parts and different CH shapes (elliptical in (c)), convex in (d), concave symmetric in (e), and concave asymmetric in (f)). Panels a–c refer to small CHs, which are commonly found in the disk centre, and plots d–f refer to large CHs.