Comparison between the final (r_s, f) and initial (r_s, i) scale radii of the clumps simulated in Sect. 5 when modelled as a Plummer sphere, as in Eq. (15). The initial scale radii are computed from the size-mass relation of Sect. 2.1. The final scale radii are obtained fitting a Plummer density profile to the final snapshots of the simulations of resolved clumps in a spherically symmetric Sparkler-like system (Sect. 5.1, circles) and of the simulations including the effects of a disc (Sect. 5.2, triangles). The dashed line is the 1 : 1 relation.