Humidity Differentials

Hi guys. My vivarium humidity seems to differ drastically between the top of my cage and my bottom. I am using a ceramic heater in a wooden viv, and I understand that warm air rises, but at the top of my cage I am reading 55-60% but the bottom is at 40%. Do I need to block the top ventilation hole so that the warm wet air is forced to cool and drop?

Has anybody else had this problem? And if so what was your solution?

How well is the wood sealed? What are you using for substrate. Perhaps a humid box like these guys do would help you.

How are you measuring the humidity? Also, a photo of the viv would help as well.

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