What is the relationship between evalpool size and population size?

Hi,Robert, is that possible to know why the number of evalpool size is sometimes less than the population size x2 ? Like if i set up the population size as 10, i guess the number of evalpool size should be 20, which is equal to population size+archive size(=population size). However, the evalpool size showed on the board is less than 20. Is that possible to know what happened here?