Yes, the documentation on this method is sparse, yet self-contradictory.
From the explanation:
"The second point in each pair of points is a >>> 2D <<< point that gives the (u,v) coordinates"
From the example code:
pt_array[1] = Geom:: >>> Point3d <<< .new(0,0,0)

This is the point array I used in a call to position_material
pt_array = []
pt_array[0] = face.vertices[0]
pt_array[1] = Geom::Point3d.new(0,0,0)
pt_array[2] = face.vertices[1]
pt_array[3] = Geom::Point3d.new(1,0,1)
Apparently, the first two points set the location of the red pin, the next two
set the green pin. I'm still working out the other two.

This is the result I get from using the point array above...