The large helmets are for the Papercraft figures and the small helmets are for the plastic toy Minecraft figures.
The helmets fit with no need to change scale.
If you want to print even larger helmets, use the large helmet and scale it up. The smaller helmet has thicker walls so it will print fine at a small size. Paint them for the type of helmet you want and have fun!
I just added a helmet that should fit the plastic toy Creeper.
They made his head larger than everyone elses.
It might fit the Enderman too, but be a little big on him.
I uploaded the wrong helmet for the Creeper, it has been fixed.

Make sure the helmet is upside down when printed.
No need for support.
No need to rescale unless you want the plastic Creeper or Enderman to wear a helmet.
If you need help let me know.
Show pics if you print this please.
Here are some 3d printed figures with Minecraft toys and a old Faller train.
http://www.youtube.com/edit?o=U&video_id=9fYU4OyzWCg