I pulled my Stark head out of the box to check, and you were right, it actually looks a bit similar. The jaw on mine pushes up further so it's flush with the rest of the helmet. The issue is that the face plate doesn't seem to be the right size to fit well. The black mouth line is the same thickness on both heads, so there's no difference there; but the face plate on the Stark head seems a bit shorter/smaller. It fits the top/sides fine, but it's less snug at the mouth area. I even put the Stark face plate on the lighted head, and the black mouth line was a tiny smidgen thicker than with the regular lighted face plate (though it could've been my eyes playing tricks on me). Either way, it does seem to be because of the design of that head.
Of course, I can now never unsee that, so the helmeted head will probably never see the light of day again.