Just to chime in here.
famousgamer, one thing that appears to be getting over looked in this on-going discussion is not so much the stock position but the relative height of the center of the sighting optic that is being used as it relates to the stock.
In this picture...
The two sights are different, which impacts how the shooter would have to view it. Specifically, the one with the left, the sight doesn't appear to be mounted but rather just sitting on the top of the marker. I don't see a rail for the scope to attach to, however, I could be wrong. Either way, it's a lower mount.
The picture of Spec.Ops is definitely sitting higher and thus his head position is different.
So it's an unfair comparison if you ask me.
This discussion is completely ignoring the fact that tilting your head is typically needed when using firearms; it's called stock weld, to get proper eye alignment. But again, if the optics are higher, so is your head position. Unless you can get directly behind the marker, like your bottom four examples, there WILL be some head tilt. If you want to reduce the amount of head tilt simply increase the mounting height of your optics as they relate to your stock.
Side question for who ever took the picture of the guy on the left. Is he really left handed? I couldn't put my finger on but after looking at the picture for a couple of minutes it dawned on me his head position looks very odd. He has his left eye WAY behind his right. That makes me think he's right-eye dominate and just holding the marker left handed. That alone would account for the horrible head position.