emailed books will ALWAYS be marked as Personal Documents, Amazon applies this as a post-processing fix.
For sideloaded books, calibre will set the cdetype from PDOC to EBOK if you set
Preferences ==> Conversion ==> Output Options ==> MOBI Output
Personal Doc tag == [EBOK]
Make sure "Enable sharing of book content via Facebook, etc." is unchecked. Do this in AZW3 Output as well.
Finally, select all calibre books, hit Edit Metadata, and check the option "Remove stored conversion settings for the selected books". Otherwise calibre will cache the previous values and your settings will not apply to any previously-sent books.
Alternatively, the
[GUI Plugin] Quality Check has an option
Fix ==> Fix ASIN for Kindle Fire
You will need to sideload the book via calibre, so calibre can add a cover image to the appropriate area.