Contour maps representing the standard deviation (σ) from (13)for different values of r_w (top: 2.5 R_⊙, bottom: 3.25 R_⊙), for the classic (left) and radial (right) model, as a function of ĝ₂ (vertical axis) and ĝ₃ (horizontal axis) coefficients. The colourbar defines the variation range of σ. In addition, coloured lines enclose regions with different percentage (100, 95, 90, ...) of jets, hence magnetic field lines, which are successfully integrated. The red crosses locate the chosen minimum in a low-σ region with at least 90% of jets integrated. This minimum is found for ⟨ ĝ₂ ⟩ = −0.5, and ⟨ ĝ₃ ⟩ = 1.6 (bottom panels) – 2.0 (top panels).