I find that my position doesn't change my ability to be lucid but it does effect the type of lucidity I get and what I'm able to do. What I've worked out so far:

- Sleeping on my back:
More inclined to dreams of flight and falling. I think because I have a heavy weight behind me but in front of me is light.

- Sleeping on my front:
Generally my ability to interact with objects in the dream greatly increases. My sense of touch, and what is nearest to me has greatly increased. This would make sense because at the moment in the waking world I feel the bed and the weight of my body. It's a very grounding type of lucidity. The only annoying thing is waking up and my arm has gone dead and I spend 20 seconds or so working out if what I'm feeling is actually my arm and laughing at how funny it feels to try and move it again.

- Sleeping on my side:
Generally gives me a mixture of different types of dreams, I find I'm a lot better at using my legs in these dreams, walking, skateboarding, things like that all become more of the highlight of that dream. It would make sense because my legs don't lay straight, they sit bent a little bit and get a mixed feeling of weight and freedom.