Status bar scaling question
 

So i had an idea for a cast bar for the UI I'm making. I have a graphical element that goes around the unit frames. I'm attempting to use that same element as the cast bar so it changes the color of the graphic around the unit frame.

I'm am able to load what is essentially a background as a status bar through shared media. The problem that arises is that the cast bar has to be scaled extremely large to make the texture cover the panel art. As such more or less half the bar is invisible until it "reaches" the texture.

I attempted to scale the bar to the size of a status bar texture. Do i need to have it the literal width (which seems to be 256) for status bars for it to fill properly?

The canvas is that size the actual image is not however.