Joe, no redirection of the bass from the mains to the sub occurs in general in that situation. Most receivers have a setting(LFE+Mains, Both, Double Bass, etc.) which applies only when the mains are set "Large" and which would duplicate the lowest bass from the mains to the sub so that both the mains and the sub would be reproducing it(not a good idea in my view).

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Enjoy the music, not the equipment.