σ-rejection contours in metallicity–opaque pressure level (P_opaque) space from our PLATON retrievals for Eureka! (top) and Tiberius (bottom) reductions of the combined (left), visit 1 (middle), and visit 2 (right) data. The 1σ, 2σ, and 3σ contours in 2D are indicated. The mean molecular weight at 1 bar in an isothermal atmosphere with HD 15337 c’s equilibrium temperature is shown on the top axes and corresponds to the metallicities on the bottom axes, computed using PLATON assuming C/O = 0.59 and thermochemical equilibrium. Minimum allowed clear-atmosphere metallicities for the more constraining datasets are indicated by the vertical dashed lines, while the maximum allowed P_opaque values at lower metallicities are indicated by the horizontal dotted lines.