MB4 218b: Tzuras Hapesach (362:10-11)

A tzurat hapetach eruv doesn't work in an area such as an area of open fields (בקעה) that isn't an inhabited area.

How wide can a tzuras hapesach be?

What is a tzuras hapesach vis-a-vis eruvin?

Positioning of the horizontal post vis-a-vis the vertical posts.