On the mappers, you can set these properties to make one appear on top of another.
ActiveMapper->SetRelativeCoincidentTopologyLineOffsetParameters(0, -66000);
ActiveMapper->SetRelativeCoincidentTopologyPolygonOffsetParameters(0, -66000);
ActiveMapper->SetRelativeCoincidentTopologyPointOffsetParameter(-66000);
LinesMapper->SetRelativeCoincidentTopologyLineOffsetParameters(-1, -1);
LinesMapper->SetRelativeCoincidentTopologyPolygonOffsetParameters(-1, -1);
LinesMapper->SetRelativeCoincidentTopologyPointOffsetParameter(-1);