Just thinking.....
I am not sure how much it matters if you keep it at 30-40% humidity. I read that I need to keep it at 50-55% and 65% the last 3 days. It seems that everyone and every article has a different opinion of the optimum temp and humidity. I have no idea who is right.
Just think-how well can a chicken regulate the humidity when sitting on her eggs? I am sure that it depends on factors outside the chicken's control- rain, heat, etc.
This is what I tell myself when stuff goes out of whack.