In the text-book example of CP violation in the kaon system, the usual statement is that the KS decays much faster than the KL because the phase space is larger for a decay into two pions, compared to three pions. (See, for example, Griffiths or "Modern Particle Physics" by Thomson.) I was wondering if that is the only large contribution. Doesn't a third pion add at least two gluon vertices to the highest-order Feynman diagram? Can this be neglected in comparison with the phase space?