A Google AdWords API Help thread estimated position or average CPC being returned by the AdWords API differs from that of the Google Keyword Tool.

Eric Koleda from the Google AdWords API Team replied basically pointing fault at the tool.

I validated that the Google keyword tool does not change the estimated position or average CPC when you change the match type from broad, exact, or phrase types. Logically, it would make sense that this means the keyword tool is off when reporting on those factors and narrowing the results by match type.

It seems if you want to get more accurate numbers for estimated position or average CPC you would have to use the AdWords API.

Forum discussion at Google AdWords API Help.