Humidity tray is different from a watering tray.
A humidity tray needs to seveal inches in diameter LARGER than the pot the plant is in. Fill it with rocks, glass beads, or something similar, then add water to just below the top of the rocks. Put your plant centered in this tray. If you don't want your plants feet getting wet, keep the water level of the humidity tray below the bottom of the pot. This allows the evaporating water to humidify the air a few inches around the plant itself, without creating too much humidity for the room. I know a lot of orchid fanatics use them all the time as most orchids like high humidity.
I'm finding with my flytrap I can use the humidity tray as a watering tray as well, just move enough of the rocks out of the way to put the pot into the water for a while, then pull it back out once it's well watered, put the rocks back, and set the plant above. It helps me control the moisture level in my medium really well, as well as creating that extra bit of humidity (and I'm finding with how often I need to refill the tray that my suite is very dry- which is strange for Victoria
)