Just better clear something up about wind angles. The true wind is not changing direction significantly the higher you get up your mast. The true wind speed is however changing significantly, as you said, because of wind shear/the boundary layer. In other words the wind closer to the water surface is affected by friction and slowed down compared with the wind up higher.

Since a boat always moves at an angle to the true wind an apparent wind is created. Apparent wind is what you feel across your face while sailing. The apparent wind angle changes significantly as you move higher because the wind speed higher is faster. A thing called vector addition lets you calculate the apparent wind speed and direction very simply as indicated here:

Apparent Wind Calculator and Diagrams

The guys at the twisted flow wind tunnel are the gurus when it comes to apparent wind and required twist. There is a diagram that perfectly shows what is happening to the apparent wind at this link:
Twisted Flow Wind Tunnel - Auckland

Anyway, enough from me.

Nick.