The rules seem to imply that a flying creature does block LOS as any, and is protected from sight (for attack and spawning purposes) as any.
But it is said that a soaring creature (which includes all flying ones) is above the ground at all times, excepted when attacking in melee.
How can one conciliate this with the above ?
Badly in other words.
Its clearly a case of KISS where extra rules were considered too complicating. Along with pit LOS its one of the few places where it is truly hard to argue a thematic answer.
And BTW, are you allowed to attack a flying creature when it flies over an obstacle, and it is allowed to attack from there ? (and does it depend on the type of attack)
Q: Do things that block line of sight when traced through block line of sight into (or out of) their own spaces?
A: Line of sight is only checked between the originating space and the target space. Things that block line of sight in either the originating space or the target space do not count. A figure with Fly or Acrobat on a rubble space may both attack and be targeted. Special rules (such as fog) may change this general rule.