@ares, for the simple example of A > B > C, then yes we see both.  However, for multiple  branches, the ancestor_ids is a always straight line up, but the opposite direction, subtree_ids, is not always the same path down.
A
  --B1
    -- C1 - D1 - E1 
  --B2
    --  C2 - D2
  --B3
    --  C3 -  D3

If my current location is B1, I see the ancestors (A) and descendants (C1, D1, E1), but I don't see B2, B3, C2, C3, D2, D3.  However, If my current location was A, then I would see all.  Does this make sense?