Hey Mrai,
First off, check out this post on relative humidity, it's pretty helpful and explains why the RH percentage is not always the value to go off of.
http://www.cigarbid.com/...-and-Cigars#post4575097 Second, have you properly seasoned your humidor? I have had issues with this in the past and I have found that purchasing the 84% Boveda packs, 1 for each 25 cigar capacity of the humidor, works really well. Just set them inside the humidor, close it, and no matter how much you want to check it, leave it closed for two weeks.
Third, invest in a digital hygrometer that can be calibrated. for 20 bucks you can pick up a digital hygrometer and a Boveda calibration kit. This is key to knowing what the RH is in your humidor.
Finally, If you're using Boveda packs in an airtight tupperware, it should be able to maintain +- 3 % of what the Boveda is rated at. I use 4 69% 60g Bovedas in my tupperdors that each have around 80-100 cigars in them. The temp is usually around 66 degrees F and the RH hangs from 66-67%.
I hope this helps.