Can't find valid references in Mullion faces

[clog boy]

I'm trying to write an auto dimensioning plugin for Revit, and have been breaking my head all morning over one hurdle.
Basically what I want to do is get all mullions that run in a certain direction (vertical or otherwise), and get references from all faces perpendicular to that direction.

            FilteredElementCollector mullions = new FilteredElementCollector(doc, wall.CurtainGrid.GetMullionIds())
                            .OfCategory(BuiltInCategory.OST_CurtainWallMullions);

            Options options = new Options();
            options.ComputeReferences = true;
            options.View = doc.ActiveView;
            options.IncludeNonVisibleObjects = true;

            List<Face> validFaces = new List<Face>();
            foreach (Mullion m in mullions)
            {
                if ((richting == Richting.horizontaal && m.LocationCurve.GetEndPoint(0).Z == m.LocationCurve.GetEndPoint(1).Z)
                    || (richting == Richting.verticaal && m.LocationCurve.GetEndPoint(0).Z != m.LocationCurve.GetEndPoint(1).Z))
                {
                    GeometryElement ge = m.get_Geometry(options);

                    foreach (GeometryInstance gi in ge)
                    {
                        GeometryElement ige = gi.GetInstanceGeometry();

                        foreach (GeometryObject igo in ige)
                        {
                            Solid s = igo as Solid;

                            if (s != null)
                            {
                                FaceArray faces = s.Faces;

                                foreach (Face fa in faces)
                                {
                                    if ((richting == Richting.horizontaal && fa.ComputeNormal(new UV(0, 0)).Z != 0)
                                        || (richting == Richting.verticaal && fa.ComputeNormal(new UV(0, 0)).Z == 0))
                                    {
                                        validFaces.Add(fa);
                                    }
                                }
                            }
                        }
                    }
                }
            }

I then want to get certain references for sot elevations (the top and bottom mullion face of the entire curtain wall) using this code:

            Richting richting = Richting.horizontaal;
            List<Face> faces = ValidFaces(wall, richting);

            BoundingBoxXYZ bb = wall.get_BoundingBox(doc.ActiveView);
            Reference r;

            if (faces != null)
            {
                foreach (Face fa in faces)
                {
                    foreach (EdgeArray ea in fa.EdgeLoops)
                    {
                        foreach (Edge e in ea)
                        {
                            XYZ pt = e.AsCurve().GetEndPoint(0);

                            if (pt.Z == bb.Min.Z || pt.Z == bb.Max.Z)
                            {
                                r = e.Reference;

                                XYZ origin = pt;
                                XYZ bend = new XYZ(pt.X + 0.5, pt.Y + 0.5, pt.Z);
                                XYZ end = new XYZ(pt.X + 1, pt.Y + 1, pt.Z);
                                XYZ refpt = pt;

                                using (Transaction tx = new Transaction(doc, "Kozijnmaatvoering"))
                                {
                                    tx.Start();
                                    SpotDimension sd = doc.Create.NewSpotElevation(doc.ActiveView, r, origin, bend, end, refpt, true);
                                    tx.Commit();
                                }
                                break;
                            }
                        }
                    }
                }
            }

("Richting" means direction, I've made an enum object to make my code branching more readable).

The code reaches the command to create the new spot elevation without errors, and I do manage to extract a reference from the face. But the spot elevation is not visible. Can anyone tell me what I'm doing wrong?

EDIT: I realize that the topic title isn't accurate anymore, but I edited the post a couple of times after some more research.