Ablation: A+B interaction: joint counterfactual vs sum of marginals
E_full MAE: 0.01490180566906929
Marginal A (SH) delta: 0.02179749310016632
Marginal B (opacity) delta: 0.12344483658671379
Sum of marginals: 0.1452423296868801
Joint delta: 0.14422519132494926
Interaction residual: -0.0010171383619308472
Interaction fraction: -0.0070030435626007885
Verdict: non-additive