I was half right... I predicted Joyce would hold one end of the chain, even though I predicted it would be Rikk on the other end.
As for the 10 foot chain point: Either (A) the rift is less then 10 feet below the edge, (B) Allisin's chain can size shift, or (C) Rumi expects Joyce to use her jet pack to lower them to a point where Joyce is less then 10 feet above the dimensional bung hole.
Actually, I suspect B: We've seen Alisin wear that puppy is a belt, then as a weapon... and it seems longer as a weapon.
(Joke suggestion for Allisin's County Song: Chain of Love)