I've masked the foreground arm in the below image, i'm trying to get a nice edge. It's either too sharp with a minimal dialate/erode with around a minus 10 pixel feather when seen above light background layers, or it's like the below image with a sharp minus 25 feather so it leaves a black border because it's eating away at the alpha channel which has been created with the mask. Is there a node setup which will leave a nice, maybe even a slightly transparent edge so it blends better with background layers underneath?