In light air (less than 5kts), the air is usually in a state of laminar flow. The air at water level is essentially at a speed of 0kts and linearly increases to the overall flow speed of the air mass 10-20m up. Maintaining adequate twist is really important in these conditions.

Depending on temperature, pressure, humidity, and a few other variables, the wind trips turbulent around 5-6kts. Then you get a lot more mixing. Then you need more camber and much less twist.

Bethwaite has a big section on this in his 1st book.