Best place to set the evaporative humidifier?

[greenpassion]

I have ordered a large room evaporative humidifier. I already have two smaller ultrasonic cool mist humidifiers running in this large kitchen living room area where I have many orchids and several other house plants. I have forced hot air heat, and one heating duct in the living room. My question is since there's hot air blowing up through this heat duct would it be beneficial for me to place the evaporative humidifier next to the heat duct? Or should I have it across the room.? I purchased this because even with two small cool air mist humidifiers it's a struggle to keep the humidity up without using a pot on the stove. I want to be able to have the room right around 50% humidity throughout this winter. And I'm hoping these three units will do it. The room is not closed off. One end of the room opens up to a hallway that leads to bedrooms. the other part of the room opens up to the staircase that goes to the upstairs. it would be so much easier if it was just a closed room but it isn't.