It doesn't make any sense to divide the efficiency by population. I have no idea what meaning to assign to the resulting numbers.

For example, imagine a country of efficiency of 1 and a population of 1m, and therefore having an "efficiency per million people" of 1.

Now, that country splits into two countries, each of population 500k. Oh happy days, each half of the former country now has an "efficiency per million people" of 2.