Although I can't give you any exact answer since I'm not an SEM expert, doing a verbatim search[1] will give you better results[2]. Though you might already be aware of how to do that (but even if so, someone else might not and find it useful). I just add it as a custom browser search[3] using the following URL template to do a verbatim search without having to click on options in google search:

https://encrypted.google.com/search?q=%s&sourceid=opera&...

Where %s will be your query.

[1] https://support.google.com/websearch/answer/1734130?hl=en

[2] https://encrypted.google.com/search?safe=off&client=oper...

[3] http://www.makeuseof.com/tag/create-custom-search-engines-go... (for chrome)

[3] https://support.mozilla.org/en-US/questions/780073 (firefox)

[3] http://my.opera.com/community/blog/2009/01/16/custom-searche... (opera)

[3] http://operawiki.info/CustomSearches (some premade searches that add just by clicking, may work on other browsers, but not sure)