Comparison of the Fermat potential posteriors between two different model settings for the LENSTRONOMY composite model. The blue solid distributions correspond to our primary model settings. In the test model setup (black dashed distributions), we fix the triple Chameleon profile for the stellar mass and light distributions to best fit values from a separately optimized model with the power-law mass profile. We also mask the central region of the deflector galaxy in the test model setup. Additionally, the prior on the halo mass profile is different. Whereas we adopt a prior on the NFW scale radius r_s in the primary setup, we adopt a combination of priors on M₂₀₀ and M_⋆ in the test setup. Despite multiple differences in the model settings, the Fermat potential differences are consistent within 1σ with each other.