I think the fact that people are at around 70% correct after a day of puzzling means that the difficulty level is pretty good. Just don't give up, the last 30% isn't as hard as it may seem. Or course the fact that you don't know which 30% is incorrect makes things more tricky... But I'll up the hints later if necessary.

If anyone is working away on this quietly in the background and think they might get it without any hints then maybe say so and I can try to be less helpful to everyone else