If u have a cushion for the temperature (upper limit ) 27 degree Celsius-induce heat , that’s always reduces the humidity - is it 55% with the lights on or off?
If your dehumidifier is a mini, Peltier style 55% is about the limit of it's ability. To get the humidity lower with a dehumidifier will require a compressor type.
55% is not bad. unless your in flower.
Can always try to cycle your air in the tent more frequently if your air outside the tent is lower in humidity.
Good Luck.