Assuming the semantics make sense, your content can still be rated as relevant for the shorter phrase as well as the longer one. To rank well is definitely a higher hurdle to clear, in most situations. it's very common only to rank for the longer phrase for a long time.
Eventually (if the site continues to grow and appeal to its visitors) ranking for shorter phrases is a real possibility. However, it may take more pages about the shorter phrase which I assume is more general.
Google has a major set of patents for what they call "Phrase-based Indexing." You may find that this technology opens your mind to new ways of understanding document retrieval in Google, including how they may score relevance. See [webmasterworld.com...]