I have found a way that is easiest for me to control the humidity. I quit using the channels in the bottom of the bator. Humidity is controlled by the amount of surface area of water you have in the bator. I tried various sized plastic containers of water in the bator until I found the right size and quantity. Containers are much easier to fill than the channels under the eggs, under the turner. For my Hova 1588 I use two containers. One will keep it between 35%-45%. When I add the second one, it goes up to 55%-65%. I have found this to be a lot easier that the channels. It takes some expirementing, but once you get it right, it's great!
BTW - For my LG it takes four containers to get the high humidity.
ETA: That's pretty cool, we both know exactly the science behind humidity control, but have oppisite ways to control it. Best thing is, both methods will work effectively.