χ² cuts at fixed Z values (upper row), and along the valley with low χ² values (lower row), for X = 0.739. The points in the lower row correspond to the minima in the upper row. As can be seen, a definite minimum appears even within the valley with low χ² values. Z values are shown in legend, and only the values for which the optimal X_c/X is in the range [0.5−1.0] are shown in the lower row.