It's getting there. Should be within a week or three. It's warming up enough and I am clearing junk out of my painting booth this coming week, so cross your fingers for me. I have some things that are higher priority to finish, but it should at least get primed and sanded a few times.
As I said back on page one, the guy who sculpted the helmet originally, did so as close as he could over a cast of his own head, which he said was on the large side. Your head circumference puts you on the line between small and medium hat sizes. I'm about an inch bigger around, and solidly in the "Large" size category, but I also have what milliners call a "long" skull shape -- longer front to back than side to side. This, as opposed to the "standard" head shape that is, while not exactly symmetrical, more balanced between the two. So I'd say large to extra large, depending on head shape, would fit an accurate one of these. So it's no wonder you find them too big.
I know they're pricey, but have you ever tried on a Don Post RG helmet from the '90s?
My head is 56cm as well. but as Inquisitor Peregrinus inferred, circumference is just a part of the fit. If you read back to the first page of posts, IP said that the original prop from the movie brushed the cheeks and nose of the actor when they put it on. The one I printed at 100 percent fit exactly like that. The mask I recommended is not 100 percent screen accurate, but it was accurate enough for my need. If one was to wear a helmet like this, a somewhat elaborate flat ducting system would need to be installed so that you would get enough Oxygen and remove the Carbon Dioxide. I don't need it myself. The helmet is just going to sit on the shelf with the others.