In most Orthodox Ashkenazi schuls, it is customary to have a lectern (the amud) at the front of the room, below the duchan, from whence the baal tefillah leads. Typically, I have noticed that it is also customary to place a "pulpit" directly in front of the amud for the rav's sermons. However, I have also noticed in some schuls that there is also a pulpit on the back-side of the bimah, directly opposite the shulchan.

What is the purpose of this second pulpit in such schuls and why is it not in sufficient to have just the one on the duchan?