So you did not read my book (http://sncf231e.nl/gauge-and-scale/) mentioned before in this thread?
Relevant paragraph:
Larger gauges are in general used for tracks in public spaces. Among the larger gauges are 9.5 Inch, 10.25 Inch and 15 Inch were the approximate scale would be 1:6, 1:5 and 1: 4 respectively. The scale used with locomotives in these larger gauges is indeed approximate and seldom accurate. Of course, the wagons used, which carries 1:1 scale passengers, are also not to scale. But the sight of a 15 Inch Pacific locomotive with its train on the Romney, Hythe and Dymchurch Railway in the south of England is breathtaking. The picture shows the RH&DR locomotives Southern Maid and Winston Churchill while being prepared for the days run.
Regards
Fred