Calculating the Distance between the Top of the Window and Row 1

@Malcolm Sokol
Please review my comment immediately below yours.

I downloaded Chip Pearson' userform positioner and have a few observations. It is highly dependent on the mode of the Excel Window. The behavior of the positioning is different when the window is Full vs. normal mode. In the latter instance, if I position a window and resize it even to a very small part of the desktop on which it is open, the form position varies all over the place even though his for displays the same values for the positions he uses. Not sure this will allow an absolute certainty of position. In a recent application I just had to offset the command bar width to the cell top position to get the location as you noted and go with that.

My Excel Toolbox includes the following function to determine the screen coordinates of the top-left corner of the first cell in a range:
Public Function Range_ScreenXY(rTarget As Range, _
    Optional sUnits As String = "pixels") As Long()
This function returns a base-0 Long array XY() with 3 elements:
XY(0) = rTarget's original ActiveWindow.Zoom before adjustment (see below)
XY(1) = screen X-coordinate for rTarget.Left
XY(2) = screen Y-coordinate for rTarget.Top
Optional sUnits specifies the units of returned screen coordinates; only the first two characters apply and alphabetic case is ignored. The following sUnits are recognized: "pixels" (default) or "pi" or "px", "points" or "po" or "pt", "twips" or "tw". Pixels are screen pixels, not Windows' pixels, which might differ; see the DisplayScreenMetrics macro.
If necessary, ActiveWindow.Zoom will be adjusted to the nearest multiple of 5 (like 75, 80, 85...); otherwise, results are close but randomly unreliable. Results are best if Zoom > 65. If necessary, ActiveWindow will be scrolled southeast (SE) to make room for a dialog box at X-Y. This function accommodates Split with or without FreezePanes (unlike Pearson's, which might not handle Zoom either).
Note: UserForm position is based on the top-left corner of the screen (not the program window) in points (not pixels).
Note: Microsoft documentation is incorrect for PointsToScreenPixelsX/Y methods, which are reliable only when their argument is zero; see http://microsoft.wmlcloud.com/forums/t/120412.aspx.
Here is an example macro that uses Range_ScreenXY to position a UserForm:

Sub PositionUF()
    Dim UF As UserForm1, rSele As Range, sAddr As String
    Dim XY() As Long, nZoom As Long
    Const Msg = "Using the mouse, select a cell to position the UserForm." _
        & vbNewLine & "Click OK to continue or Cancel to quit."
    Const Title = "PositionUF"
    Const AdjustX = 6 'determine empirically for your configuration
    If TypeName(ActiveSheet) <> "Worksheet" Then Exit Sub
    nZoom = ActiveWindow.Zoom
    Set UF = New UserForm1
    UF.StartupPosition = 0
    Set rSele = Selection
    Do While True
        sAddr = rSele.Cells(1).Address
        Set rSele = Nothing
        On Error Resume Next
            Set rSele = Application.InputBox(Msg, Title, sAddr, Type:=8)
        On Error GoTo 0
        If rSele Is Nothing Then Exit Do 'user clicked Cancel
        XY = Range_ScreenXY(rSele, "points")
        UF.Left = XY(1) - AdjustX
        UF.Top = XY(2)
        UF.Show vbModeless
    Loop
    Unload UF
    Set UF = Nothing
    ActiveWindow.Zoom = nZoom
End Sub

See https://sites.google.com/view/MyExcelToolbox