I found a way to draw rectangles around whatever cutree cuts, so I think I
now have a better idea, which is that it looks for the largest k distances
and cuts there, where k is the # clusters you want defined. Then, I assume
Dunn index uses the same defined #clusters to determine within vs. across
cluster similarities (i.e. distances).
If I'm way off please let me know, otherwise thanks for taking the time to
read my question.
kbrownk