Rood, you're correct that Fellaini played 'in midfield', but are mistaken in certain respects when using your stats. Fellaini's average position can be affected by a lot of different things during a match, such as the quality of opposition and their style of play. And I haven't seen anyone in this thread say he didn't play in midfield, they just said that more often than not, Fellaini played as the furthest forward of a three.
You also have to remember, as you said, that you looked at '5-6' games, which is a fairly small sample size and you don't provide context as to who the opponents are. It might have been that Everton relied on counter-attacks while giving up territory and possession, so the more mobile Osman was relied upon to make runs to support the striker, despite being the more central player.
That being said, from what I saw, Fellaini more often than not was used behind the striker and certainly did not screen the defense, and Ross Barkley has just taken over from where he was, albeit with a different style.