Mine did the same in my tubs for the first week.

How long have you had yours in there?
Is there a water bowl in the tub too?
Do you have any holes drilled in the tub currently?

I added a few more holes in my tub, made sure the unit wasn't wet in any way, and gave it a week. The percentage started dropping once the air flow (from the holes) improved. Now it sits nicely at about 70%. It does tend to rise to 80-90% when I refill the water bowls though, then drops by that evening back to 70%.

My guess is that you just need a few more air holes and to give it a chance to settle. It seems to take these units longer to adjust to humidity than it does to adjust to the temps.