This is a png in which there is the blood with the alpha channel. When I drag this decal on to shiny metals materials I continue to get this border. I am pretty sure I am making the alpha map correctly (as this decal looks fine on not-reflective non-shiny surfaces)
The problem seems to be in the metallic property. After lowering the metallic property by .2 the borders were gone. I have no clue why that is. Any Idea?
Nothing you can do about it without modifying engine shaders. Just try to have the transition be as short as possible on that channel to reduce the problem a bit.