SUMMARY I would like to see a future version of Plasma move the volume and brightness OSD away from the center and to the bottom of the screen (or perhaps have it be easily user-configurable?) In my opinion, this will make the popup less intrusive, due to it being more "out-of-the-way" from any content.
KWin controls OSD positioning; moving there.
*** Bug 462584 has been marked as a duplicate of this bug. ***
The position of the OSD along the y-axis is very odd indeed, and it would be nice to see it moved further down.