Deuteron-to-proton (top panel) and $^3$He-to-proton (bottom panel) yield ratios as a function of the average charged-particle multiplicity density. All yields are measured at midrapidity, i.e., $\left|y\right|$ 0.5 for pp, Xe--Xe and Pb--Pb collisions, and $-1\left|y\right|0$ for p--Pb collisions. Statistical uncertainties are shown as vertical lines, whereas systematic ones are shown as boxes. The coalescence predictions are shown as bands, whose width represents the model uncertainty. The black and green lines correspond to the expectations of two different hypotheses of the CSM.