Dynamical-friction timescales for clumps of mass 10⁶, 10⁷, and 10⁸ M_⊙ (dashed, dotted and solid lines, respectively) as a function of the distance from the centre of the halo. The red-dashed area covers the range of dynamical friction timescales relative to the interval of clump masses and distances of interest. The grey horizontal line corresponds to the look-back time at z ≈ 1.4 t_lb = 9.23 Gyr, that divides the plot between the region in which the dynamical friction is most likely inefficient (t_fric > 9.23 Gyr) and efficient (t_fric < 9.23 Gyr). The latter is marked by the grey area.