Schematic diagram showing how the slope of the ⁵⁶Ni distribution determines the relative importance of the diffusive tail. In both the top and bottom panels, a luminosity L ₅₆( t′) would be produced at time t′ from the diffusion wave probing the ⁵⁶Ni distribution. In the top panel, the slope of the ⁵⁶Ni is shallow, which produces a shallow slope for L ₅₆ (shown by the red curve). If a diffusive tail luminosity is drawn back from this point (shown by the purple curve), it always falls below the ⁵⁶Ni light curve. Thus, the diffusive tail from this depth is not important. In the bottom panel, the slope of the ⁵⁶Ni distribution is steeper. Therefore, the diffusive tail from larger depths overpowers the heating from ⁵⁶Ni at shallower depths, and the diffusive tail from this depth impacts the light curve.