When my turtle was smaller he always slept in the plants near the top of the water. Since I moved him to his new bigger home I only see him sleeping on the very bottom. I wasn't sure if he was too heavy now for the plants or if he wasn't finding a comfy spot. I haven't seen him sleeping in his hammock at night yet, but during the day I have seen him in it with his head sticking out of the water.
Its either an adjustment period or preference. I notice that my male RES likes to sleep atop the heater (where the thermostat is) and leave his head out. The first few months he was in there, he'd sleep on the bottom of the tank.
I love this idea! My turtles are too big to float on the fake plants now and I've been trying to think of something for them to rest on towards the top of the water. This looks great!