Elli -- As quoted by Joshua above, DeWitt says that the letter to Menoeceus is composed in a different "style" of Greek writing than are the other two letters. Do you agree that the letter to Meneoceus seems more "elegant" or is written in a different style of grammar?
QuoteDeWitt on page 12 holds up the letter to Menoeceus as (alone of the extant letters) "composed according to the rules of rhythmical prose". Epicurus in this one letter is writing artfully.