Radial profiles of the temperature gradient ∇ in 2.5D simulations with N_r = 512 and the boost factors given in the legend. The gradients are normalised using the adiabatic temperature gradient ∇_ad. The curves are derived from simulation data averaged over the time interval 0.3τ_th ≤ t ≤ τ_th except for the b = 10³ simulation, for which we use the interval 0.3τ_th ≤ t ≤ 0.5τ_th. MESA models with α = 0.0 (our initial condition) and α = 0.6 are shown for comparison. The inset zooms in onto the convective-penetration layer with dots marking the location of the steepest gradient in ∇/∇_ad.