Upper panels: Comparisons of the evolution of the strength of $\sqrt{ \langle\langle \Delta p_{\rm T1}\Delta p_{\rm T2} \rangle\rangle }/{\langle\langle p_{\rm T} \rangle\rangle }$ with produced charged-particle multiplicity densities, $\langle {\rm d}N_{\rm ch}/{\rm d}\eta\rangle$, in Pb$-$Pb collisions at $\sqrt{s_{rm NN}} = 5.02$ TeV (left) and Xe$-$Xe collisions at $\sqrt{s_{\rm NN}} = 5.44$ TeV (right) with calculations using the HIJING and AMPT models. Lower panels: Ratios of the model calculations to measured $\sqrt{ \langle\langle \Delta p_{\rm T1}\Delta p_{\rm T2} \rangle\rangle }/{\langle\langle p_{\rm T} \rangle\rangle }$ Solid symbols represent the measured data with statistical (vertical bars) and systematic (boxes) uncertainties. Model calculations are shown with shaded bands denoting their statistical uncertainty.