are you making the width changes in the menu writer wizard?
If you change the width in the menu writer wizard, it should also change the offset of the submenu items.
When setting a width for the main level items, you should set a width in pixels. you have 6 menu items on the top level, so use 160 for the menu item width (960 / 6 = 160) to fill the full 960px width of the page.