Not massively familiar with blender and looking at: https://docs.blender.org/api/blender_python_api_current/bmesh.utils.html?highlight=edge_split#bmesh.utils.edge_split
It's not clear what the value of the 'fac' argument is supposed to be? Is it a 3d coord? (x, y, z) or something else, like a fraction of the total length of the edge?
What's a good way to calculate it? As examples there's this: https://github.com/lijenstina/mesh_extra_tools/blob/c90634a024ab8d531751df873d33dbe905d0ca13/mesh_extrude_and_reshape.py#L217
But want to confirm calculating the distance between the edge's two vertices is necessary.