The 2.5 is already ordered by morphman, so it is ordered in the way that is easiest to go through with i+1 as much as possible. So card one has 1 new word, card two uses that word plus another new word and so on. If you went by frequency (the other way you can order it) you'd get a bunch of cards that use 5 new words and have a very uneven learning experience.
Edited: 2016-04-22, 4:22 pm