Combined $\chi^2$ profile for the extraction of the correlation volume for baryon and strangeness conservation obtained by comparing the normalized second order net-$\Xi$ cumulants and the $\rho_{\Delta\Xi\Delta K}$ in Pb--Pb collisions to the Thermal-FIST predictions. The region close to the minimum $\chi^2$ is shown in the inset. The dashed line represents a fit to the $\chi^2$ profile with a fourth-degree polynomial function.