Coefficient of Friction
Corners: Ideally, friction has nothing to do with surface area of the materials involved. The assumption that makes this so is that there is no interference (grab) between the surfaces. The coefficient of friction is the Tangent of the angle that the pieces must be inclined to in order for slippage to occur.
And, the coefficient of static (non moving) friction is higher than the coefficients of dynamic (sliding) friction. This is why once slippage occurs, it does not stop.
But in real life, there is interference. As in wide tires on your car provide more traction than narrow ones. And so on. Lots and lots of real world situations where surface area is related to forces required to effect movement because there is "grip" between the parts.
An extreme case is velcro.
So in real life, surface area is usually a big deal involving friction. Really.
The 99S's use of 15 crosses instead of the more normal 18 results in less mating area between strings and thus interstring friction which lets the mains slide more easily out of position and then snap back.
Chicago Jack has a thread relating to coefficients between various strings that is very insightful.