do not try to adjust the hum and water at the same time
what I do for initial set up with LG is set temp first with no water in bator.. set it to 102F
then add water and see what hum% is..
If you ever run out of water during hatch, the temp will spike to only 102F
another thing I do is duct tape the top to the bottom
You might also try marking the top and bottom so that you always put them together exactly the same each time.. and take the top section and put it into place on the bottom section and press own slightly and slide the top around to sort of sand the seal between the two of them..
Don't forget that your chicks are absorbing the fluids in the egg which will drop the humidity and also will make the temp go up a bit. Where is your thermometer in regards to the fan and air flow? I agree about the above post!
Since I'm working on an experimental bator instead of a pre-made I have three thermometers and two hygrometers. Two read and show me the temps at both ends, one accurite inside for wiggler temp and hygrometer and a flukers (reptile) dial hygrometer.
Sponges on end do produce more humidity.
I really think the idea of stabilizing temps at 102 before any humidity so that dry it doesn't spike is a great one.
That last week can get very weird as chicks draw moisture and produce their own heat.
Jars sealed with water can really really help to stabilize temps.
If you tend too high - one of those ziplock square containers filled with rice, cut a few holes in the top or leave it open. It absorbs some moisture and provides thermal mass as well.
The rule of hatching is simple when you think you have it all figured out- something weird happens.