Halliday & Matthiessen (2014: 376-7):
The principal difference is that experiential Epithets are potentially defining, whereas interpersonal ones are not. … Even in the superlative …Note that, in general, the same word may act as either experiential or interpersonal Epithet … there are very few words that serve only an attitudinal function.Interpersonal Epithets tend to precede experiential ones.