how do i use BoundingBoxIntersectsFilter to find floors intersecting with stair BoundingBox

[pnoZFP35]

I'm trying to find the floors my stairs is going to and from

 

I am using BoundingBoxIntersectsFilter to find the floors that are intersecting with my stairs BoundingBox. when I then find the floors I want to take the one with the highest Z value, and save it to "Upper slab ref". And the one with the lowest Z value and save it to "Lower slab ref".

And now to the problem when I try to do this I will get to many floors or non at all

how can I make it so it will always find the right floors, in any given situation.

The middle stair will get 4 floors

The highest stair will get 2 floors but non of them is from the upper floor. and the lowest stair will find non at all.

code is shown below 

ICollection<Element> AllStairs = new FilteredElementCollector(doc).OfCategory(BuiltInCategory.OST_Stairs).WhereElementIsNotElementType().ToElements();
                FilteredElementCollector collectorSlab = new FilteredElementCollector(doc).OfCategory(BuiltInCategory.OST_Floors).WhereElementIsNotElementType();
                
                foreach (Element el in AllStairs)
                {
                    IDictionary<string, double> StairsSlab = new Dictionary<string, double>();
                    List<string> allSlabs = new List<string>();
                    BoundingBoxXYZ bb = el.get_BoundingBox(doc.ActiveView);

                    Outline outline = new Outline(bb.Min, bb.Max);
                    BoundingBoxIntersectsFilter bbfilter = new BoundingBoxIntersectsFilter(outline);
                    collectorSlab.WherePasses(bbfilter).ToElements();

                    if (collectorSlab != null)
                    {
                       foreach (Element e in collectorSlab)
                        {
                            BoundingBoxXYZ location = e.get_BoundingBox(doc.ActiveView);
                            double zPoint = location.Max.Z;
                            allSlabs.Add(e.Id.ToString());



                            StairsSlab.Add(e.Id.ToString(), zPoint);
                        }
                    }

                    if (StairsSlab[allSlabs[0]] > StairsSlab[allSlabs[1]])
                    {
                        tr.Start("Reload");
                        el.LookupParameter("Upper slab ref").Set(allSlabs[0].ToString());
                        el.LookupParameter("Lower slab ref").Set(allSlabs[1].ToString());
                        tr.Commit();
                    }
                    else
                    {
                        tr.Start("Reload");
                        el.LookupParameter("Upper slab ref").Set(allSlabs[1].ToString());
                        el.LookupParameter("Lower slab ref").Set(allSlabs[0].ToString());
                        tr.Commit();
                    }
                }

[jeremy_tammik]

Are you just trying to determine the top and bottom floors reached by the multi-storey stairs? If so, I can imagine there is an easier way to do so than what you describe. For instance, is it not possible to determine the stairs' maximum and minimum vertical Z extents? Then you can easily eliminate all the floors in between those two values, and determine which of the two left over is the upper and lower one.