Thanks Guido,
Raising humidity is exactly what I'm doing with the old soda bottle, you don't need it enclosed at the top because humid air is heavier than dry air so it sinks and stays in the bottle.
I asked this over two years ago and I can say that the solution worked great

However now it's in a glass vase (again open at the top) and the hook of the mount hangs on the side of the vase.
There are decorative stones in the bottom and always water in the bottom. Sometimes the base of the mount sits just in the water a the mount wicks the water a little. It likes that as well.
The plant hasn't tried to turn up towards the light, it seems to grow fine downwards. It's latest leaves are bigger than older ones which I take as a good sign, and if's flowered lots of times in the last two years. In fact I have a couple of photos of the last flower I keep meaning to post.
I think the mount is getting a bit old though now after a two years, it's cork and it's starting to crumble. I think I'm going to re-mount it soon.