Which end are you taking the measurements on and what are the temps on either end? Is the lid solid or does it have an area cut out for a lamp? Is the water bowl over the heat source? Just curious as it's odd to have that kind of struggle in tupperware. I used to have to run the DIY humidifier when I had Kali in glass (big 'ole Gatorade bottle) to keep the humidity up and ensure the air was getting exchanged enough to not stagnate (not a good thing). Neither has been a problem since upgrading her from glass. Any way you could maybe post a shot of the setup?