On my desktop I have two panels - the first (with the system tray and a clock) is in the right corner and visible all the time, whereas the second (with the contact list applet and the presence applet) is on the right side - more or less centered - and autohidden. They are both shorter than the desktop. When I connect an external screen (which is to the right of my ntb) and make it the primary one, the right panel change its position to the uppermost right corner.