You will also need to check for other EMDs using the same four keywords in a different order, these may be competing for authority for the four words but only Google knows for sure.
Scrapers, feed repeaters and the like are also to be checked out as they often automatically re-publish content on a per keyword basis and you might be triggering several of them.
example: Google the very title of this post and you will see it posted verbatim on another site already, automatically. While this post outranks that post they are still 1 and 2. That effect is more intense with more competitive keywords.