Struggling with non-rectangular shader

I’ve a side bar with an opaque image and behind it, a separate object with a blur shader. I’ve elected to curve the image bar but I’m unsure how to adapt the shader to a curve, it otherwise stays rectangular and doesn’t follow the curve (image panel 1 & 2). If I apply the shader directly to the image, it goes black. If I apply a curved image to the shader layer, it too goes black (image panel 3). After poking around at the obvious options and sliders on the shader/image layer and further playing with adding masks and such, I’m unfortunately not getting anywhere.

I saw a similar resolution to this elsewhere up here, but their solution was to change the canvas to worldspace, but for other reasons, I cannot change my canvas from overlay. I am green with shaders so apologies if I’ve missed an elementary application/technique to resolve this. Any help is appreciated, thanks.

Modify the shader so that it only affects the pixels with a texture opacity over say 0.1? Just off the top of my head, I think that would work