FM receivers exhibit a behaviour known as "capture", in that when they receive interfering signals they tend to pay attention to the strongest and ignore the weaker ones. This is often observed with commercial broadcasts where you may hear two competing AM stations at the same time but rarely do you hear two FM stations together. Since DVOR uses an FM signal it benefits from this capture phenomenon and rejects the weaker reflected signals, where CVOR using AM would detect a combined signal with a combined phase that is decoded into an incorrect bearing.