${\rm D_{s1}^+}/\Ds$ (left) and ${\rm D_{s2}^{*+}}/\Ds$ (right) ratio times BR as a function of the average charged-particle multiplicity \avdndeta in pp collisions at $\s= 13$ TeV at midrapidity ($|y| < 0.5$). The experimental results are compared with the theoretical predictions based on the SHM, the SHMc, PYTHIA 8, and EPOS4HQ. The statistical and systematic uncertainties on the measured ratios are depicted as vertical lines and boxes, respectively. The theoretical uncertainty on the predicted ratios is depicted as a shaded band for the ${\rm D_{s1}^+}$.