Constraints on wall shape parameter w under the restriction of y = 0. The plot shows the excess of the best-fit χ² for a given w with respect to the global minimum , which is normalized by the threshold value Δχ². The color-coded curves represent each individual epoch, whereas the thick black curve is obtained by combining all four epochs. The vertical dotted line marks the best-fit value of w from the unrestricted analysis, which coincides with the values obtained under y = 0. The bottom panel shows the well fitting range and the best-fit value for all five analyses.