[maximalmobi7]

**
The cover thumbnail will be downloaded directly from Amazon. The Kindle needs to be online.
**
thanks for the above information, so I fixed the asin number to match an ebook version on amazon.com website, but since it was linking it to an real book asin number instead of the ebook version, I don't no if it would download that thumbnail image since again I am not taking my device online for thumbnails, that's why I use calibre again to transfer both ebooks and their thumbnails to the device, so it may or may not work,

-- but I want to keep my device offline that why I use calibre in the first place for transferring ebooks, otherwise my device would be spamed with amazon web ads, which I don't want on my device, so I just keep it offline, calibre has no problems transferring the thumbnails of mobi and azw3 to the device, so I may wait for the kfx ebook format to come more smaller and once calibre has an native kfx converter if that ever happens without requiring an plugin option. also may wait for it to be more stable with less converting errors from the epub source, since rb format doubles the output size I think. it may not be worth the kfx format if you have to have the output size bigger than the epub file size was to start with.

also the size of the files are as follows , the kfx file format was converted from rb book

epub file 6,913
azw3 file 7,126
mobi file 6,982
rb file 12,861

the azw3 and mobi was kindleunpack with that under calibre, so your seeing its split file sizes

kfx file 17, 388

kfx file 17, 387 is the size when the kindle ids: tag matches an kindle ebook instead of real asin amazon book from web link under calibre's ids: metadata

I don't no if the kfx file is just bigger since I used the rb book source, or if it could be smaller and their no way yet to split out the mobi and azw3 formats from the output that I can tell.