However, I did not have the advantage of Stephen's book to know how to stand correctly, which makes a difference to the regularity of your shooting. I must add that thin strings are used with lighter bows. I wouldn't use a ten strand string with a thirty kilogram bow. However, the thickness of strings is more influenced by the material and its strength than the preference of the archers. The material must be strong enough to take the impact of the release of the bow.
Some materials are bulky, but light.
Others are durable, but heavier. Some just don't occur in your area. Luckily from the archaeological viewpoint, arrow nocks are the perfect gauge of string thickness. We know precisely what thickness of string both the Ancient Egyptians and the Scythians used, thanks to preserved arrows.