The point of a humidifier is to up the RH in your grow space. Find a place where all the room can have almost the same moist level.
I usually place it in the middle, but I have custom noses to shoot horizontally at 360° for the early veg stage, and when I introduce fans in the box, I made the humidifier nose face it (the wind will disperse the droplets).
Don't worry about your plants getting wet, the fan will move leaves and water shouldn't stay long.