I had same problem. Mine would stay at 83 percent. Didnt matter with Aspen, Newspaper or paper towels. I even had a lid with holes and plenty of holes on the side. Nothing mattered.
I then researched here and was told I was golden. That having 83 percent humidity would not be a problem and that I didnt need to do anything unless the humidity got so high that there was condensation showing up on the tub.
When I needed to lower humidity though I had to turn on my ceiling fan. That was the only thing that lowered it. Extra holes, holes in the top different substrate nothing else would lower it.
I currently maintain 73 percent with my fan set at low, but I kept it for weeks and weeks at 83 and based on what I was told here, it would have been fine.