Comparison of the actual predicted kinematics from the modeling of the physical three-dimensional mass distribution κ_λint (Eq. (35)) for varying core sizes (solid) and the analytic relation of a perfect MST (Eq. (25), dashed) for the mock lens presented in Fig. A.2. Lower panel: fractional differences between the exact prediction and a perfect MST calculation. The MST prediction matches to < 1% in the considered range. Minor numerical noise is present at the subpercent level (https://github.com/TDCOSMO/hierarchy_analysis_2020_public/blob/6c293af582c398a5c9de60a51cb0c44432a3c598/MST_impact/MST_pl_cored.ipynb).