I wish you hadn't mentioned that it is your model railroad, as I'm confident I would never have known it wasn't the real thing. My wife also didn't know until I told her.
Based on my experience and the descriptions at the Helicon Focus website, I'm surprised you used Method C. Did you try using the default settings (Model B, Radius 8 and Smoothing 4)? If so, what was wrong with the results?
If you're not familiar with the information about when to use a particular method, be sure to check out
https://www.heliconsoft.com/helicon-focus-main-parameters/