If you want to get an appropriate understanding regarding the relationship between your earnings and viewership, try to understand it from the investors (person who uses Adwords) point of view.
If the investor is sure to get redirects from potential buyers from a particular country, his adwords campaign will be directed towards that country alone. And a click from such a country will surely yield more CPC (return) for you.
For example, if the investor is sure that a viewer from USA is most likely to make an actual order, he will encourage such viewers (hence google will also encourage such viewer from USA), but if the investor is sure that the viewer from Pakistan (where even Paypal is banned) will do nothing and he/she is just a burden on your site. He will never encourage such a viewer. Hence generally a return on such a click will only hurt your CPR.
Moreover, the click (return $$$) also depends upon action. If the viewer of your site is redirected from your site (via adsense ads) to a particular site where he actually makes some order. you will get a higher return.
From my personal experience of 5 years with google.
My highest click (yet) was from USA . That was around 4.2 $
And my clicks from pakistan, india, bangladesh etc are aroung 0.01 - 0.05 $.