1) I am working in Windows 8 with the Export to Kindle plug-in.
I am working to a Kindle page size of 1280 x 800 landscape mode.
I have set up my InDesign CS5.5 page to the same size and I am placing images this size.
When I create a .mobi file and load the file into my Kindle Fire, the page is smaller with a large border of white around the image.
2) I create an image that is 1280 x 800 pixels. When I bring the image into the page, the image comes in smaller and I have to use Fit Content Proportionately to fit the image to the page size.
Am I doing something wrong that the image is not the correct size when I add it to the page?
Have you tried to export to EPUB and then convert to MOBI?
A lot has changed in the EPUB area since CS5.5 was released.