I think you just are going to have to deal with these readings until you find a better solution. You have that acurite on what I am going to assume is the driest part of the tank on the bottom of it and on what looks like relatively dry substrate. Humidity can fluctuate by large amounts form one side to the other in these glass tanks so what might read 40% on one side could be 60% on the side with the damp moss.
I personally would not just have the moss out like that but in two open containers on opposite ends of the enclosure and the containers damp with the moss wet. This way the snake does not live on damp substrate but the moss will improve humid conditions. You still might have to mist the enclosure daily or every other day and the levels might not be where you want them but you might get them above 50%
This is also the reason why I believe that in many parts of North America, glass tanks are just a pain in the butt.