[stumped]

PS - but if you could help me get my head around the design philosophy.. by marking this attempt at a summary...
calibre treats a cover as a chunk of metadata and stores it outside of the book ( though confusingly there is usually also a matching copy inside of the book , at first anyway ). it creates the "outside" copy when book is added to library. thereafter it never changes it for that format - but some plugin do.
The database stores one cover per book , no matter how many formats exist, and it stores it as an image.
When send to disc, or convert format is called that outside cover is copied to inside the (new format ) book. No change is made to the convert from book. unless the "conversion" is an overwrite, to same format,
how am i doing so far please ?
then when calibre sends book to kindle ( by wire) , it sends only the book mobi/azw file from which the kindle firmware extracts the inside cover and uses that as a thumbnail. true/false ?

I did read the calibre help all about covers page, but that does not have all the nitty gritty details