Smith Helmet Sizing – Between sizes?

Looking to buy a new lid – like the look of Smith helmets but I’m exactly between the sizes between M and L. One reason for changing is because my current helmet is too loose with a helmet light so want something that adjusts / sits snugly. Is the helmet sizing accurate – I have a 59cm bonce?

I would be buying both from crc & sending back the one that didnt fit or trying another manufacturer if neither felt perfect.

My thoughts exactly as returns are free