Rackham requires a 1-inch margin throughout your document, but a 2-inch margin for chapter titles and major headings like Dedication and Acknowledgments. Using a Heading 1 style and redefining the style to create the two-inch margin is often the best method of doing this.
By adding the extra space above the Heading 1, you combine the default one inch margin from the document with the one inch of space on the heading to create your two inches.
Please note that you must have a "Section Break (Next Page)" immediately ahead of your section or chapter heading for the Heading 1 style to insert that additional space. If you're not getting a two inch margin, it's most likely that you're missing the "Section Break (Next Page)".
See Setting Up a Heading 1 Example on the previous page for the step-by-step instructions for modifying your Heading 1 style.