The best thing would be for epub readers to show metadata
as book jackets at the start of the book so no need to create book jackets inside the file.
I added bookjackets as my v3 readerdoesn't show synopsis in bookinfo.
To edit bookinfo I open the epub in winrar and then remove it
using notepad++ as sometimes its convenient to use the original file as I would have to reselect chapter headings and all the other things I had to do the first time
You can also use sigil I stopped using it as the earlier version used to mess up things
I haven't tried the latest versions