I don't think it's a question of what a court might find for or against you on.
It's more a question of what Fox legal will accept, or not accept.
If they don't like it, they could, and have in the past order you to take down all pictures involving their characters. There's nothing you can do about it, even if you think you're legal. Can you afford to meet Fox legal in court?
So really the question is, is anybody else getting away with doing what you want to do. If they are, then you can maybe take a chance. Even if Fox legal decides they don't like it, at that point, they'll most likely just to tell you not to do it, providing they're not also mad at you for doing something else they disapprove of. Even so, you're taking a chance, I think.
The best advice would be maybe to contact Fox legal, and ask them if they'll let you. I wouldn't be optimistic though.