Is it normal for the head of your penis to be smaller than the shaft?

My penises head seems to be smaller than the rest of it. Like from the base its pretty thick (like a 5.5in girth) but then as it goes down it gets a bit smaller then at the head its not as big. is this normal cause i hear all the time how people have 'mushroom' penises with heads bigger than there shaft...idk my dicks only like 5 and an half inches long anyway so its not like im gonna be getting anything anytime soon...