Building a house in West Lake and East Lake, can the back wall be widened?

You can't.

In our hometown, there are few yards to build houses in the countryside. According to the geomantic omen of the older generation, it is normal that the East Courtyard is bigger than the West Courtyard, and the houses and yards in the West Courtyard cannot exceed the East Courtyard. Specifically, it only refers to townhouses, and there is no such requirement for houses built independently.