Simulation setup SI: comparison between growth rates Γ₁ and Γ₂ at peak position at maximum drive time. Although the effective energy input varies by a factor 100 (see Table 4) another transport mechanism becomes dominant. The smaller peak (Γ₁) develops dominantly in the perpendicular direction while the evolution of bigger peak (Γ₂) is more isotropic and tends towards smaller k_∥. The colours indicate the logarithm of the total spectral energy.