Likelihood ratio ℓ computed for the optimistic case. Left: ℓ in the reference setup. Centre: Same as the left panel, but with R = 500. Right: Graphical explanation of the banana-shaped ℓ shown in the left panel. Each pair of values (w, σ) in the legend indicates the inverse particle mass in keV⁻¹ and the RSD displacement parameter in units of h⁻¹ Mpc, respectively. The stars of corresponding colours in the left panel serve as identifiers for each combination in the parameter space, while the red circle denotes the true values used to generate the data.