If those were my bookcases I would have books standing ( their backs against the back panel of the bookcase ) behind the books, taking up the full width of the shelves, plus a load piled on top of the case and still need room for more!
P.S. Then I would stack books laying flat on top of the shelved books to use up the vertical space between shelves, must utilise all the space you have available!!!
Ah, but these are post purge bookcases! --- And remember almost all my reading is now by ereader and the vast majority of those are Kindle Unlimited, so they do not reside long on my reader. ---- Now if my wife wouldn't keep ordering romances and filling up library with those. (sigh!) --- The worst part? Almost all my Amazon recommendations are now for stories like "The Bronco Rider's Bride." ---- Pretty good title. Maybe I should write the book?