3D scopes should magnify only the image inside the scope and not be painted onto an already magnified image.
They should also occupy much less space on the screen, around a third of what they do now.
There is no benefit in adding a "3D scope" which doesn't allow you to maintain awareness of what is happening around you.
Look, let's just get real for a second. The current 3D scopes are a gimmick. Make an object which circles the inside of the scope and magnify whatever is inside there, and leave the rest unmagnified.