STAR Collaboration
The four ESS approaches that extrapolate $\Delta\gamma^{112}$ (a--d) and $\Delta\gamma^{132}$ (e--h) to zero $v_2$ or zero $v_{2,{\rm PPOI}}$ with events classified with either $q^2_2$ or $q^2_{2,{\rm PPOI}}$ in 30\%--40\% Au+Au collisions at $\sqrt{s_{NN}} =19.6$ GeV. The distinction between the panels in each row is indicated by the title on the $x$-axis. The linear fits (dashed lines) are used to extract the $y$-intercepts at zero flow. For clarity of presentation, we combined every four data points in (b), (c), (g), and (h), but the linear fits were obtained from the data without rebinning.