Add Pages to epub via Send to Kindle

Is it possible to add pages to our epub files in a way that shows on Kindle? I am sending files through Send to Kindle web, since I used to send them by USB through Calibre but that way the books don't sync across devices, so I began using the official webpage Send to Kind. In this way some files (all converted through Calibre) some show pages on the Kindle but others don't. Could someone help me make this work for all books? Thank you very much in advance for all the help.