I have a larger head and ordered the M/L Half Dome and couldn't be happier with it. The fit is perfect. The dial on the back truly gives me a custom-feeling fit that isn't too tight but is very form fitting and keeps the helmet properly positioned. The chin straps and buckles are placed just right so that nothing rubs uncomfortably on my face, jaw, chin, etc. I can't guarantee this helmet would work equally well for every user, but wearing this makes me feel like I got a custom-fitted brain bucket for an off the rack price.