Hey Guys,
Being somewhat of a Vader nut and owning several 1:1 scale screen lineage Vader helmets(eFX Legend and the famed SL). A true 1st or 2nd gen 1:1 scale Vader helmet is pretty big once you see it in person and then have a chance to compare it to say a Don Post fiberglass helmet which is also a 1:1 scale piece. Its the whole copy of a copy shrinkage deal. This is even present on my ANH SL vs the eFX Legend helmet, even though both originate from the Rick Baker mold taken off the original screen used ANH helmet, the the SL is one generation closer and therefore slightly bigger than the eFX.
The HT helmet is closest to accurate and scaled correctly for the rest of the HT line. The Kaiyodo is slightly underscale for the other HT figs and so is the Hasbro dome. The HT Vader looks surprised because the dome sits too high and the underside of the eyelids are painted grey instead of black like they should be. I can post pics of my eFX Legend next to my RS stormtrooper lid and you can see what I am talking about.