Why not shift the heater down toward the wall? Okay please don't take this the wrong way, suggesting you undo what you've got there, but from my wire run experience I'm thinking about how versatile the mesh is - what about instead of the board (or use the board there for the mount) you use a wire mesh panel like one wall of a dog crate, or a barbecue grill or something? Hang that, then you can take two S-hooks and hang the heater anywhere along it and also adjust the height, and it's easy to put up and take down. I suggest it be close to the wall, to the right, since they want to be over there, and put it lots lower so they get all the rising heat off it.
Okay, another thought, based on how close I see the ladies here get to it - since they (Bernie) use the platform below to get up on the roost, you might think about hanging the mesh panel from the ceiling, and hanging it behind where they are now (opposite side of the roost bar), so that it can be closer to them. In this picture it would be heating their rumps. Totally in the way of your camera view, I realize, where it's placed right now.
A compromise might be to hang it on the side it is now, but kitty corner between the right wall and the window wall to get it closer.
Just a suggestion, it's all up you!