To be honest, they aren't going to seek out the platform most of the time. Them landing on it will most likely be a happy coincidence. After surfacing to breathe, it is instinctual to get low quickly in case they were spotted by a predator. They may also be showing trouble 1) because they are not the most graceful of species or 2) your tank has a current from the filter that may be a bit strong for them.

How big is your tank? Can you post a picture?