The reason for the poor div. for the exacta, when the fav. comes first and a long shot second is the same as the reason for the poor div. for the trifectas in general. I remember decent tri. dividents only a few years back, these days I could'nt be bothered with betting trifectas.
Simply, too many people put the fav. in with the field.
If you really must include the field in your exacta, then put the field for first and the fav. for sec. or bet quinella.
Good luck