Do you have Cork Bark in there?
How often are you misting?
If the Humidity is correct then they will spend more time sleeping on the glass or behind the Cork Bark Flats.
If the Humidity is low they will tend to sleep in the moist moss on the Ground.
Here is an older picture of My Crested Geckos Tank

How often are you misting?
If the Humidity is correct then they will spend more time sleeping on the glass or behind the Cork Bark Flats.
If the Humidity is low they will tend to sleep in the moist moss on the Ground.
Here is an older picture of My Crested Geckos Tank