First, the InitialChatFriendsList is the chat list that the people who are online aren't "pulled" up by Facebook. For me, it's based on many things. The people who likes, comments your stuffs, views your timeline, chats with you will get a kind of score. Why a person that doesn't chat with you often will come out on top? Well, for example, person A viewed your timeline 500 times, liked and commented your stuffs 100 times each and has never chatted with you. I guess it will be 700 points but I'm not sure how many points will Facebook give. Person B chatted with you 500 times, viewed your timeline 20 times, liked your stuffs 10 times and never commented, this made it 530 points. Person A wins, therefore he will be higher than person B in the chat list (in offline mode of course) or InitialChatFriendsList. Sorry for my English, hope it helps! :)