Apologies, I didn’t look closely enough at your original post before answering.
You’re right that there’s something screwy about the Edge Collision behavior when you reduce the height below a certain amount.
The way I would do this is with an Oscillate behavior on the Y Position Transform set to Half Range, using a Ramp behavior on the Amplitude to gradually reduce the bounce height. That way you can position the result wherever you want very easily.
https://www.youtube.com/watch?v=GbiGRlhkpN8
The Half Range option means that there will be a “collision” effect at the bottom.
Here’s how I’d set it up:

Notice that I’ve adjusted the Phase (from the default of zero) so that the “ball” starts off screen at the top.
Simon Ubsdell
http://www.tokyo-uk.com