yes, don't have any standing water. the water should be 1-2cm below the lowest point of your substrate. if you have standing water on the lower parts in order to keep the higher parts moist, you will either get mold or the plants in the parts standing in water will melt in a few weeks.
depending on the size of your tank, you can keep the half with the slope covered tightly and have a 'varied' humidity throughout. this will probably not work on smaller tanks. I had a glass lid covering 3/4 of my 40gal with the back part that had the slope completely sealed. however, I had a pretty steep slope as well and the very top of the slope would dry out within 1-2 hours of misting. I ended up just leaving that part bare...not going to try to bang my head against a brick wall.