The analogy doesn’t work for me. Regardless of distance or distribution unless someone has changed the definition since I studied biology then by definition two animals who can produce FERTILE offspring MUST be of the same species. That would mean that “Neanderthals” who could interbreed with Cro-Magnon and produce FERTILE offspring were of a different species than the “Neanderthals” who could not do so. It would also mean that those “Cro-Magnon” and “Neanderthals” who WERE able to breed and produce FERTILE offspring were in fact of the same species regardless of what name they are called by. A St. Bernard dog and a Chihuahua are of such different sizes that they could probably never interbreed naturally but by artificial insemination a St. Bernard female could deliver puppies fathered by a Chihuahua male and they should be fertile and able to reproduce. This is because both are simply different breeds of dogs, NOT separate species in spite of the tremendous difference in size and appearance. On the other hand a Lion and a Tiger can produce offspring but the offspring will not produce a line of descendants because Lion and Tiger are two different species in spite of their similarity in size, build and predatory nature.
Making, of course, the assumption that Homo Sapiens Neanderthalensis and Homo Sapiens Sapiens really are different species.