As far as I know ive always had a large dip in my skull where my soft spot would have been. Im a 62 yr old female. Because its so lg, ive asked many others if they have this. Ive not found another like mine. A lg mans thumb could lay in the spot in my skull.
This can happen both congenitally i, e from birth or can be acquired due to various reasons. But from the way that you describe the dip with no other features or symptoms this should not because to worry. But if u do have some symptoms this may have to be investigated but if it is just the dip with no other symptoms till date u can leave it alone. Some people may acquire this during birth in a normal delivery