Injection threshold speeds for V_s = 1500   km   s^-1: the classical threshold u₁ (solid curve) versus our reflection threshold (dashed) and the threshold for injection after downstream scatterings (dotted, v > v_Tμ−). Protons within the shaded areas have nonzero injection probability; the different shading represents the injection possibility through reflection, downstream scatterings, or both. The classical threshold overestimates the lowest injection speeds, especially at small shock-normal angles.