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If you sharply turn a baffle corner, there is a pressure change that sends a reflection back at the listener, which arrives late and causes a comb filter frequency effect. If you turn that same corner, and instead of finding a single 90 degree sharp turn you pass over two 45 degree sharp edges forming a bevel, you create two such filters. The distance to the median point between those two edges is the center of a notch-filtering band. The distance between those edges is a width of notch effect. The item filtered by that notch filter is the cancellation of the comb filter like warbling. In all actuality, it is a beat frequency pattern, not a notch at all. The first nodal destruction is a half wavelength sum and the periodicity is every harmonic thereafter. But it still resembles a notch-filtered band, and as that is the way it appears when you view its effects in the frequency domain, so I improperly refer to it as a notch filter.

So. If you sharply turn a baffle corner there is a reflection that comb filters. If you turn that same corner with a two sharp edges forming a bevel you create two filters. The distance to those two edges is the center of a notch-filtering band. The item filtered by that notch filter is the cancellation warbling. For that narrow region there is significant cancellation of the comb filtering effect because there is a destructive phase alignment of the two reflecting filters. Above that frequency and below that frequency you see increased evidence of the combing effect. Below that region the phase difference is not significant (they remain correlated) so the two reflections sum more or less. Above that region the phase difference is again changing with frequency and so appear to be uncorrelated, so they sum and difference at the harmonics of the notch but for only tiny frequency windows and with only a modest amplitude effect in total.

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