Why was the early sedan chair in Tibet so small

The road is not good. According to historical records query shows that the early Tibetan roads are difficult to travel, the larger the sedan chair needs to lift the sedan chair, the more people, the more difficult to pass, so the sedan chair will be designed to be relatively small, easy to pass. Sedan chair, also known as the "shoulder", is a kind of people or animals to carry, carry and line, for people to ride the transportation, was widely popular in the East and West countries, in terms of its structure, the sedan chair is mounted on two bars can be moved on the bed, chair, sitting pocket or sleeping chair, covered or uncovered, the sedan chair is the earliest evolution of the car.