If its giving you headaches it's too tight. Are you in summer ATM?
Have you ever had a bra that sort of fit. By the end of the day you were dying to take it off but for the first few hours was fine? Same deal.
It fits pretty well but not great,
I've found the most comfortable helmet I've ever worn on sale at my local saddlery 2 years in a row. 170 down to 49. I think it's a euro hunter ultimate.
The helmet I hunt in has extra foam padding on the sides as it seemed really round so I stepped up a size and padded the sides.