I was hatching with 25% humidity in mine. Again the state wants moisture higher. they want 50% and 65% at hatching.
I had to add a second water tray to mine and I am only at 45%. When I was at the 25% I simply put a piece of plastic (hard plastic) over half the water tray.
Also the air holes in the back will adjust the humidity. Just do not close them completely (IMHO) the chicks need air too.