The List Tuning is the second tab in the Contextual Related Posts settings screen and provides you options that allow you to fine-tune the items in the related posts list.
Number of posts to display
Maximum number of posts that will be displayed in the list. This option is used if you do not specify the number of posts in the widget or shortcodes.
Related posts should be newer than
This sets the cut-off period for which published posts will be displayed. e.g. setting it to 365 will show related posts that were published in the the last year. Set to 0 to disable limiting posts by date.
This shuffles the top related posts. Does not work if the cache is enabled.
Related posts based on title and content
If unchecked, only posts titles are used. Each site is different, so toggle this option to see which setting gives you better quality related posts. Sometimes, lesser words will give more relevant results.
Limit content to be compared
This sets the maximum words of the content that will be matched. Set to 0 for no limit. Max value: 2,000. Only applies if you activate the above option.
Post types to include
At least one option should be selected. Select which post types you want to include in the list of posts. This field can be overridden using a comma separated list of post types when using the manual display or the shortcode.
Limit to same post type
If checked, the related posts will only be selected from the same post type of the current post.
Post/page IDs to exclude
Comma-separated list of IDs to exclude from the list. e.g. 188,320,500. This applies to posts, pages or any other custom post types.
Comma separated list of category slugs. The field above has an autocomplete so simply start typing in the starting letters and it will prompt you with options. Does not support custom taxonomies.
Exclude category IDs
This is a readonly field that is automatically populated based on the above input when the settings are saved. These might differ from the IDs visible in the Categories page which use the term_id. Contextual Related Posts uses the term_taxonomy_id which is unique to this taxonomy.