Thanks for the feedback!
I didn't want to put the border horizontally to leave the player with a choice in some parts of the game, whether they would like to try to get heals or whether they want to just get rid of the shrooms from a distance. I didn't want to force in a specific way to play the game. And as for the shrooms being dumb and getting stuck on corners, I'm aware of this problem, same with the huge damage area of the melee shrooms.