i was just thinking... ...what if you'd double the height of those indicators and then move them downwards, just enough so an indicator would appear as it would be coming from under the dock and starting to crawl onto it. a darker color or gradient on the bottom half of that new indicator might emphasize that impression even more.
i like a lot the preview image, man. although the icons could be a little more in line, perhaps. .. but the overall background works great with that dock and creates an even more 3-D impression.