i have dents in my forehead too. in fact, all over my skull. you might just be noticing them now because you are focusing on your skull. after feeling again, yes, my brow ridge--barely noticeable to the eye but very noticeable if you feel my forehead--kind of feels like dents, right where my helmet sits.
as a community organizer, i agree with the opinions expressed by the engineer and the photographer. it's not your helmet.