As I've progressed through nightmare, I've noticed that public quests past a certain point are not available for me to join despite being well beyond that quest(currently I am able to join only up to "Trailing the Coven" on Nightmare despite clearing that act). I assume this is because I am not within the listed range of levels allowed for those quests.
So, is there a list of these level requirements so that I may know how much further I must level for my quest progress to be in sync with the public games I can join?