The "factor" in coincident topology resolution has no effect in vtkOpenGLPolyDataMapper v9.0
In VTK 9.0, no matter what value the factor argument is set to in calls to these APIs:
the rendering doesn't change.
Searching the code and tracing in the debugger shows that vtkOpenGLPolyDataMapper::GetCoincidentParameters() returns the factor value that was set properly calculated, taking into account the global and the relative values.
However, the code that calls it never uses the factor. Only the units/offset value is used in vtkOpenGLPolyDataMapper::SetCameraShaderParameters() to program the shader program.
There is no documentation to indicate this and the units value is insufficient to properly handle coincident lines and polygons. See the attached image of how edge lines and outline lines inside a polygon volume of an unstructured grid are visible at the interfaces of actors with coincident polygons.
This wasn't a problem in VTK 8.2.