Hello, I think it should end with the counter as well. Keep it the same height at the pieces below the window in that area. From a function point of view, a backsplash is to prevent water from damaging the wall. Since it's behind the sink, this would be a good thing to consider. The plug is in an odd spot. If you don't need it, I would remove it or just move it somewhere else. It won't look good to have the last tile cut in half at that point.