It’s all over the place, but I think that’s the reality. Latex and mass production is just that way.
My head measures just a tad over 22" on my forehead, so my head is small/medium (according to fitted hat sizes). The 2018, which I got the originals of back in 2018, is pretty snug even for me, but wearable.
I also got the original H2 back in 2012, and it was pretty big but at least with big, you can wear a stocking cap, add some foam, or add velcro on the back.
My original '78, from 2019 I believe, is the biggest mask I have, almost unwearable even with a hat and velcro. It displays nice on my life size Myers, but still looks a tad big.
All the original H2 and '78 that I’ve bought over the years were all large masks- I got 3 of each as I rehaul them (for fun). The newer “yellow” H2 mask might be different, I think it’s just a little smaller but still not a small mask. I know TOTS made a “Small H2” for like a year, but that one is really hard to find and might be too small.
So I agree with you, they vary a lot and I can’t see TOTS changing sizes much as (now I don’t know) I think that would require making new molds-? I might bring a soft tape measure if I go to Spirit again this year to measure one, but that’s hard to do when the hair is on it (and an inside dimension is impossible).
I’d love to think they shrunk the '78, but until they say (and I think they would advertise it, knowing people want a smaller one) I just think it’s normal variations and/or people just have a hard time comparing sizes when they only vary at most 2-3" in circumference. And their hair could be longer/shorter, or their head shape in unique, etc…
If I knew the '78 this year at Spirit was for sure verifiably smaller, I’d definitely pick one up as it’s a great mask- but I already bought my mask for this year and I got the TOTS Frankenstein as it’s going out of production (lost the license) and it is an amazing Boris Karloff likeness. But I have been known to make poor budgeting/financial decisions, especially when it comes to the Myers hobby!