I can hazard a rough guess but it is only that. Seems like phase cancellation occurring at 64 degrees on the RM setting. The multiplication of a carrier wave by the ring mod process has a tendency to produce a sort of amplitude pulsing, which to some extent could be similar to a delay effect, so I guess due to routing (don't have a Virus FX routing diagram in front of me) the RM is canceling the delay effect but not the dry signal?
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