Humidity comes from the surface area of the water, not the depth. So you might want to try cut sponges in the other channel so you can add or subtract sponge pieces until your humidity gets stable.
The air in your house might be really dry this time of year due to running your furnace.
The 20 is totally different. In the winter it takes both wells just to get to 40%. Be careful filling them all the way, it will leak when you turn it. You just have to do 3/4 and fill them more often. You can close the vent halfway to help, too. I've run it 1/4 open in a the winter with no issues. It takes a paper towel to wick water at lockdown, that's the only time I wish I had a pump, but I've always hatched that way with great hatch rates
I didn't even think about closing the vent hole. I noticed there are 4 holes in the bottom yellow part. Probably for water over flow but I thought they also may help with ventilation. By any chance, do you know if you can add a humidity pump to my model?
Kahlua is wonderful, French vanilla flavor. Yum
Biggest complaint about the 20 is keeping humidity up.
Remember, depth doesn't increase humidity. For lockdown you can add a paper towel under the basket, draped through the wells, so it adds surface area and wicks water from the wells. Fix up a tube thru the vent to add more water as necessary when that time comes.