What you say is correct Macljane - to a degree!
If you look at all the 5 letter answers, these are in alphabetical order, just for the 5 letter answers.
Similarly the 6 letter answers are in alphabettical order, just for the 6 letter answers.
The only answer (from memory) that did not follow this pattern was POLK which was not in alphabetical order of the 4 letter answers.