Ok there was a limit that was making it so you could not see all of the png. I have upped the limit to the screen size. So you will soon be able to
use any size/shape popcase.png. You will also be able to add a layout.ini file to the albumpop folder to set the position of the cover within the png.
I tested with your graphic and the layout.ini that will work with yours is:
[CoverPos]
X=449
Y=143