It's really hard to compare sixth scale vs movie stills as there's so rarely a full shot of a character, and obviously there are different humans under the suits, where the figure has one stock body and for the most part that's what we see in most people's photos. And then on the sixth scale end of things, so many photos have lens distortion, etc. where in those all the heads are too big.
Maybe Solo_Bones is onto what I'm seeing and it's more the bodies than anything else for me. And again, I don't think the bucket is hugely oversized or anything. Just seem a touch large compared with the body to what I have in my mind's eye. The HT Stormtrooper/Sandtrooper bodies always looked a bit vertically compressed to me, so that might be more what's going on--proportions between the upper torso/frame of the figure compared to the helmet.
I'll see what I can come up with later as a comparison.