Hope everyone is having a great Christmas! I have a humidity question.

I have seen it posted on here and on other sites, and it does seem that the practices around humidity seem varied.

I didn't mention it above, but out tank is an 18x18x24 Exo Tera. We have a 2inch HydroBall layer separated by basically window screen and ABG mix substrate with leaf liter of the top. We have a Zoo Med HydroTherm probe/controller to help keep a constant temp/humidity level, but the issue we are seeing is the humidity plummets from 78% (that is the setting I have on the HydroTherm) to the mid 50% range in a few minutes and then the ProMist is turned back on and it mists back up to 78%. Rinse and repeat and the Substrate has started to get really really wet. I noticed this morning when I replaced the water dish with a smaller one that the sub straight was overly wet so I unplugged the pro mist and began reading all I could find again on maintaining humidity in a terrarium and saw several people suggesting to cover some of the mesh top with a towel/ plastic wrap/ glass basically anything to help trap in heat and humidity. So off to the store we went and bought some picture frames and used the glass to cover 80% of the mesh top.

The humidity is still sitting at 54% and the Pro Mist is still off. I am hoping that the heat in the terrarium mixed with the plants and the wet ABG mix will naturally increase the humidity some. Is there anything else we can do to get this under control a bit more?