An investigation into the mechanism by which v30 enhances intramolecular vibrational energy redistribution in S1 p-difluorobenzene is presented. Calculations based on our previously presented model for the anharmonic coupling constants show satisfactory agreement between the calculated and observed enhancement in state mixing caused by v30. This model sets all models equal with respect to the magnitude of the coupling constants, leaving the vibrational quantum number dependence of the operators the sole mechanism responsible for the calculated enhancement. It is the very low frequency of v30 that causes the modest increase in coupling strength to be manifest as an observable increase in the IVR state mixing. This mechanism is not unique to v30 nor to p-difluorobenzene, and thus very low frequency modes in other molecules should also cause an enhancement in IVR.