vtkCaptionActor2D and the size of Leader glyph

I am using vtkCaptionActor2D to create an annotation on a volume dataset; I liked the idea of the “leader glyph”, and played around with it a bit, but could not get the automatic sizing working for my case: when setting the camera rather close to the attachment point, the leader glyph is extremely small, and therefore not visible:

only when zooming out a lot, I see the glyph:

My code (sorry that it’s not a full MWE at the moment, I did not yet have time to prepare one):

	vtkNew<vtkCaptionActor2D> capAct;
	capAct->SetCaption("Annotation 0");
	vtkNew<vtkArrowSource> leaderGlyphSource;

Am I doing something weird here?

When looking at the size adaptation code, I found it peculiar that the code just takes the middle display point and computes the distance of 1 pixel in world coordinates.
On a hunch, I took the attachment point instead, converted that to display coordinates, add +1 in x and y direction and converted it back, and used that distance for scale factor creation:

    auto p1 = this->AttachmentPointCoordinate->GetComputedWorldValue(viewport);
    // get world coordinates of point 1 pixel away from attach point:
    viewport->SetWorldPoint(p1[0], p1[1], p1[2], 1.0);
    double dispPt[4];
    dispPt[0] = dispPt[0] + 1;
    dispPt[1] = dispPt[1] + 1;
    double p2[4];
    if (p2[3] != 0.0)
        p2[0] /= p2[3];
        p2[1] /= p2[3];
        p2[2] /= p2[3];

Now it looks as expected - the leader glyph stays roughly the same when resized:

Also regarding the “arbitrary” factor of 1.5 factor - I think a “more correct” value there would be the square root of 2 as the diagonal length of a unit cube?

Another minor nitpick: I find the name LeaderGlyphSize confusing - since, as specified in the doc, it is not a size, but a factor to the size of the glyph itself.