The group meters, along with the target/implied target decrease just like normal bars. Although you raise in interesting question as to whether it's possible to make them drop from two different ends, mirroring each other.
Here's a screenshot from ingame that hasn't been cropped or altered so the size aspect can be felt accordingly. The resolution is 1280x1024. Of course, it would look better in a higher resolution, but that's the highest I can go on my monitors.
