Function RadiusModifier.CalculateCircleInner

bool CalculateCircleInner (

Vector3	p1	Position of first circle
Vector3	p2	Position of the second circle
float	r1	Radius of the first circle
float	r2	Radius of the second circle
out float	a	Angle from the line joining the centers of the circles to the inner tangents.
out float	sigma	World angle from p1 to p2 (in XZ space)

)

Calculates inner tangents for a pair of circles.

Add a to sigma to get the first tangent angle, subtract a from sigma to get the second tangent angle.