Boss difficultie increase by number of player ?

I just got in an argument with my friend about the bosses difficulties, i say that the bosses difficulties are on par with the number of player like aspect of the night would have less health and damage if you are playing with 2 people instead of 3, but he says that its easier at 3 people than 2, which is fine but now im curious about if the difficulty scales with number of players or not