Combined dependence of the projection distortion ratio 𝒞(N, SDR) = ⟨ℓ_3D⟩/⟨ℓ_2D⟩ on sample size N and SDR. Left: ensemble-averaged measurements from 1000 fractal realisations with D = 1.7–2.5 and n_div = 2–4. Centre: best-fitting three-parameter model 𝒞_∞[1 − e^−SDR/S₀](N/100)^β. Right: fractional residuals (𝒞_meas − 𝒞_fit)/𝒞_fit. The fitted parameters (𝒞_∞ = 1.94, S₀ = 21.8, β = 0.17) capture the joint behaviour across two orders of magnitude in both variables. The model converges to the geometric projection limit (𝒞 ≃ 1.3) for small well-resolved samples and to the beam-limited regime (𝒞 ≃ 1) when SDR ≲ 10.