Good points, SL.
There are some features that are not obvious at certain angles, and then there are features that at certain camera angles emerge and then you go, "What the--? I didn't see that there a moment ago!" And that's what you deal with when dealing with an organic shape of three dimensions.
The right neck flare, the right jaw droop and the left skull buldge. As much as people have blasted the Don Post Deluxe for having these features, they *DID* appear on the screen-used helmet in the Tantive IV scene of Ep. IV, if you look carefully enough. You see the neck flare when Vader comes on board the Rebel Blockade Runner, and then looks down at the corpses -- looking from one side to the other. As he tilts his head downwards, the right neck corner is quite visible.
Anyways, when Vader has been used in promo shots, if they reverse it, notice that they omit the breathing box, because a flipped breathing box is a dead giveaway. This may not always be true with the movie, but there are certain shots in ESB when Vader is fighting Luke at Bespin where Vader is flipped.
I don't remember if this one was flipped or not, but if it is... then I probably flipped it.