Shooting the dragon's head with a bow allows you to deal more damage

During the dragon fight, if you shoot the dragon's head hitbox (even if the hit doesn't register) it makes you do much more damage to the dragon. I am not sure if this is a bug or if it is intended. Below I have linked an example of it in use (I could not attach a video because of the file size):

https://youtu.be/CZUhrkj6PMc