Lower humidity?

Simple things you can do is defoliation and remove some of your fan leaves to improve airflow. Also your RH will adjust depending on how much moisture you have in your medium. If you are using hydro try to use less water in your res and if you are using soil maybe try to water less. These are small changes but may be able to lower your RH a few %. Hope this is helpful and all the best with your grow!

Does the exhaust dump back into your room or do you extract it outside entirely? My humidity dropped from 65-70%(higher when lights out) to the 40s simply by rerouting my exhaust out my flue.