We'll create fresh WordPress site with cbnet Different Posts Per Page installed. You have 20 minutes to test the plugin after that site we'll be deleted.
This plugin will allow you to customize the number of posts, orderby, and order parameters for all index page contexts, including the blog posts index, search index, and all archive indexes (category, tag, taxonomy, author, date, archive). Orderby settings support all values relevant to archive index pages, including none, ID, author, title, name, date, modified, rand, and comment_count. Order settings support ASC and DESC.
Note: Plugin settings can be configured via Dashboard -> Settings -> Reading.