Comparison of the observed (panels a) and b)) and modelled (c) and d)) properties of the bifurcated trailing component (BTC) in J0437−4715. The observed properties (I and Π in a); ψ and log I in b)) present a zoomed part of Fig. 3. The arrow in b marks a step-like change in PA at the centre of the BTC (the PA is shown with dots). A similar step-like change in PA (solid lines in panel d) occurs for a one-sided emissivity profile (η_⊥, thick solid in c)) which is decreasing gradually (linearly) on the right-hand side, but much more steeply on the left-hand side (a half-Gaussian with σ_η = 1°). The thin solid line in d) presents ψ_⊥, whereas the thick line presents ψ obtained for a fixed fractional contribution of the O-mode: I_∥ = 0.3I_⊥(φ). This is an exemplary result obtained for ψ_B = −0.9φ, ρ_crv = 5 × 10⁴ cm.