I just tried the (lengthy) link you provided. Perhaps my brain will work it better in the morning. I think the key for me is to ask whose money was used to give over 1/2 support. If my client's disabled daughter uses her SS benefits for her own desires or entertainment, does that count as part of her support? But if the mother puts aside these funds toward her daughter's future needs (say, after she passes) then she should be able to file as HH.