Fix the page boundry size when printing to Oversize paper
When selecting an oversize page (12x18) to print on, Excel trims the printing area down to a rough 8.5x11 page area. If you select tabloid (11x17) it fills the area correctly.
Something that prints on 8 pages of tabloid shouldn't print on 18 pages of a slightly larger sheet.
See the previews in the attachments. One shows how this document would print on 11x17 and the other shows the reduced size of a tabloid extra.