Refer to figure.
The Polar Stereographic Chart Projection is a plane projection and the parallel of origin is the pole. Meridians are straight lines radiating from the pole which cut parallels of latitude at right angles. Parallels of latitude are shown as concentric circles and their distance apart increases away from the pole.

Convergency is how much the Great circle track changes, because of the converging meridians and is correct where the chart is tangential to the reduced Earth, at the pole.

Great circles at the point of tangency would be straight lines, but the tangential point is only a point, so you cannot draw a great circle there. Elsewhere, Great circles will actually be slightly curved concave to the pole, but near the pole can be assumed to be straight lines.

Thus, since the meridians at the two positions converge with an angle of 30°, then the straight line drawn between the two points will change direction by the same amount, 30°.