GPU instancing does not work when drawing Polyline repeatedly in Immediate mode

Use a class that extends the ImmediateModeShapeDrawer class.

using( Draw.Command( cam ) ) {
    Color tmpCenter = new Color(0 / 255f, 85 / 255f, 46 / 255f, 1.0f);
    Color tmpBothEnd = new Color(62 / 255f, 179 / 255f, 112 / 255f, 1.0f);
    Color tmpUnitColor = (tmpBothEnd - tmpCenter) / 10;

    Draw.LineGeometry = LineGeometry.Billboard;

    using (PolylinePath p = new PolylinePath())
    {
        p.AddPoints(polylineVts); // polylineVts is Vector3[]

        for (int i = 0; i < 10; i++)
        {
            Draw.Polyline(
                path: p
                , thickness: 1.0f / (i + 1)
                , closed: false
                , color: tmpBothEnd - (tmpUnitColor * i)
            );
        }
    }
}

In order to implement a pseudo-gradient in the horizontal direction of the Polyline, the same Polyline is drawn many times in the same frame with only the thickness and color changed.
From reading the documentation, I am aware that the above code can be drawn without regenerating the mesh.

However, in reality, changing the number of loops increases the number of SetPass calls.
When I look at the IM Monitor, it shows "1 polygon/polyline path assets", so it appears to be recognized as a single Polyline from the Shapes perspective.

(Perhaps I am not understanding you well enough)

Perhaps this kind of usage is not expected, but could you please enlighten us?