Steady state heat currents (a) J_l/γ, (b) J_m/γ, and (c) J_r/γ as a function of the coupling strength α_m. The red circles are based on the Redfield scheme; the blue squares are based on the nonequilibrium noninteracting blip approximation (NIBA); the black solid line is calculated from the nonequilibrium polaron-transformed Redfield approach. The other parameters are given as ε_l = 1.0, ε_r = 0.6, Δ = 0.6, γ = 0.0002, ω_c = 10, T_l = 2, T_m = 1.2, and T_r = 0.4.