Question about AdWords Diagnostic Tool

[bomo]

I am confused about the AdWords Ad Diagnostic Tool and its relation to average position. Next to each keyword, scrolling over the magnifying glass gives you a message of "This keyword is OK" or "Your ad is not showing on the first page". This I understand. However, I can't correlate this with avg. position. I get the "not showing" message for some keywords with an avg. position of around 3, and the "OK" message for some keywords with an avg. position of over 6. Shouldn't these be correlated? Which "measurement" is more accurate? Thanks for any advice...