Hrm... do you think the amount of water in the tray has something to do with the humidity? Cause I've filled the train with about an inch of water and now I'm starting to think that's way too much since with that much water it'll be harder to heat up with my lamp and so there will be less evaporation. How much water do you have in there?
Up to about 1/2" to the top so alot more than you, how are you measuring humidity? also if the temp where the tray is is high you won't see as much condensation on the walls of the dome. Condensation only occurs when there is a temp difference on the surface that is being condensated on. My ambient temperature in the apartment is 70-74 degrees F and the humidity stays between 55-60% (this may be a factor as well, I don't know). I have a ton of plants in my apartment so my humidity levels are much higher than most, I actually work to keep them below 60% so I don't get any mold or fungus growing on anything (now that winters coming it won't be that big of an issue).