OK, first, the taller the container, the harder I think it is to get temps and humidity right. It can be done, though.

Going without a picture, a few suggestions: reduce the space between the container and heat source, because you just need enough room for air to circulate between them, and turn your heat pad a little lower if it's going over 100. Next, you might want to scootch the heat pad over a wee bit to help warm up the cool side. Then, if your water dish is plastic, consider switching to glass or ceramic or similar. You can get a round ceramic casserole dish at wally world for just a few bucks that should work to help conduct heat and up the humidity. Finally, give it hours after making changes to see what effect they'll have before deciding if they've made a difference.

Hope this helps. Get back to us and let us know your progress.