Thank you rhody I appreciate your help. I did not originally install this modification on my forums (my admin did, and unfortunately, he is no longer with us). So I am a bit ignorant as to why things are as they are. It appears that I have only one location for horizontal banners, and that location places all horizontal banners into rotation in both locations - above the footer, and below the header. I assume my old site admin set it up so 'position 0' is referenced in both those locations? I see no option to place banners in those two locations respectively.
Here is a screenshot of the CP for the banner system. Position 0 is for horizontal banners in both positions collectively. All other positions seem to be for vertical banners.
Thanks again for your help.