Yeah this is something I've been mulling over for a while actually. Round here in Somerset we don't get many dogman reports but the ones I have tracked tend to cluster near the old Somerset and Dorset line. Disused for decades now but still a clear corridor through the landscape.
My theory, and its not original, is that these old lines follow older paths. Ley lines, drover routes, whatever you want to call them. The railway engineers weren't stupid, they took the path of least resistance through the terrain and a lot of that followed routes people and animals had used for centuries.
Whether dogman is using these as travel corridors or whether something about the geography attracts sightings in the first place I genuinely can't say. Could be both.
Anyone got specific reports tied to named rail lines? Would be good to start mapping this properly rather than just trading anecdotes.