I’ve just been playing around with the “suggested” settings that seem relevant to the “New & Unread Topics” block, and it seems that the number set in Suggested topics takes precedence over things actually being New or Unread.
Regardless of changes to Suggested topics unread max days old or Suggested topics max days old, you’ll always get X number of topics here, even if some are old and quite read:
Perhaps it would be better to have a parameter Max suggested topics and limit the list to topics that really are New or Unread?