It sounds like you know where to choose your setting for that but you mentioned that when viewing a “category”, you only get 7 showing per page, but the blog home page shows the 16 per page? I just tried this on my local test site and I was able to get the correct number of posts showing. For my themes, I don’t add any script for number of posts, so this sounds like it’s more related to WordPress itself. I’m thinking perhaps you might have a glitch. One way to test this and to see if it is the theme or WordPress, is to switch to a default theme like Twenty Thirteen and see if you get the same result.