Since you're embedding with a 'post area' within your Wordpress theme, you're really at the whims of how your Wordpress theme handles responsiveness. When exporting straight from Hype, you're getting a Hype-generated HTML page with access to the full viewport width, and the entirety of the HTML body -- no footers, headers, or percentage-based widths governed by your theme.
If you are able to create a blank Page or Post template without the responsive trappings of your theme and embed in that, this will give you a more direct representation of what your Hype document would do when previewed directly from Hype. Here's a template you can use, plucked from the HTML5 Blank Wordpress theme and slightly modified:
All this does is display the title and post within standard HTML. It also includes the default CSS reset used in Hype responsive documents to ensure the Body and HTML tags are sized correctly.