60 and 75% is ideal...
If the humidity tray does not raise it as much as you want, if you direct the fan at the tray it will spread a lot more moisture so one way or the other you will get it up if you want to.
Also when I first set up my case I was using a humidity tray, once my case was set up and filled with 60 orchids I had to start leaving the door open a little so it might be you have too few plants in there
Every time you add or take away plants things will change slighly. The more plants you have the more they will raise the humidity themselves.