Synthetic surface density map Σ derived from an analytic spiral density model simulating tidally induced perturbations in the cir-cumbinary disc of 3 Puppis. The model incorporates two trailing spiral arm perturbations caused by the binary companion. The red dashed circle marks the inner dust rim R_rim ≃ 5.7 mas (∼3.6 au at 631 pc), and the black dotted circle indicates the radius of the SE asymmetric structure R_ref ≃ 16.71 mas (∼10 au at 631 pc) inferred from the L-band MYTHRA image. Binary star positions are marked with dot symbols (purple for the supergiant star and black for the low-mass companion) scaled to the correct mass ratio and projected separation (stellar radii not to scale). The gas disc extension D_gas ∼ 4.39 mas (∼0.88 au at 631 pc) is displayed as a blue circle to scale. Both panels use logarithmic colour scaling to represent the local gas surface density normalised to 20% contrast. Left plot: Wide FoV (160 mas × 160 mas) in sky-plane Cartesian coordinates (α, δ). Right plot: Same simulation with a FoV matching the VLTI/MATISSE M-band MYTHRA image (87 mas × 87 mas).