Sketch of the ForbMod model for FR-related FDs. The GCRs diffuse into the self-similarly expanding FR (r/a = const.), which is initially empty at its centre (r/a = 0), where a(t) is the FR radius and r(t) the radial distance from the centre of the FR to its borders. As a result, at an arbitrary time after the FR eruption from the Sun (i.e. at an arbitrary heliocentric distance), a distribution of GCRs inside the FR is observed, given by the Bessel function. The relative GCR density (FD [%]) at the borders of the FR is 0%, whereas in the centre of the FR it is given by the amplitude of the depression (A_FD, max). For model details, see the main text.