You're right: the EV is 2.5 (my guess was pessimistic). For (almost all) 6-word sets, there's a single word you can use to delineate all six words, which gives

You're right: the EV is 2.5 (my guess was pessimistic). For (almost all) 6-word sets, there's a single word you can use to delineate all six words, which gives an EV of 1.83 if that word is in the set and 2 if it isn't.