There’s no such thing as “normal” when it comes to WordPress. This platform can be the basis for a giant corporation news website, as well as your neighbor’s recipe blog, which they last updated 5 years ago. All it takes is one different plugin (and not necessarily a caching plugin) and your cache headers may come out differently from the origin server, affecting how Cloudflare cache operates.
Cloudflare cache has an eviction policy that will purge cached page that are unfrequently demanded. So, for 2 websites with same CF config, the more one site is visited, the more it gets cached.
Also, Cloudflare by default caches at the edge in the colocation the page was first requested. If one of the 2 sites has a more broad audience geographically speaking, it will have a smaller cache ratio, as visitors’s requests may have gone to different CF colos…
The best you can do is familiarize yourself with how Cloudflare cache operates and make sure your WordPress installations make the best use of it.