Kim's right.

There's even a 3rd banner sidebox option: banner_box_all.

Again, you can position the banner sideboxes on either the left or the right, and you can specify the desired banner group to denote which banners will appear in that sidebox.

Banners don't just appear in the left/right columns. They need something to appear "inside of". Hence the use of the banner sideboxes mentioned.


You can of course do custom coding to alter the overall behavior if it's not meeting your needs.