VBA to set absolute position of chart DataLabel

[dbooksta]

I have an Excel scatterplot with a number of 2-point series. I am trying to set the position of each DataLabel in VBA, but its behavior is unpredictable. Here is the result, with each label text showing the (.Left, .Top) value that was set:

I would expect every label with .Left = 100 to be positioned at the same X position on the chart. But the first one is positioned horizontally in the middle, and the next four are stuck against the left side of the chart. Likewise, the .Top position is not placing them consistently. For example, (100, 250) is much higher vertically than (300, 250).

And here is the code:

Sub PositionDataLabels()
    For i = 1 To 10
        ActiveChart.FullSeriesCollection(i).Select
        ActiveChart.SetElement (msoElementDataLabelCallout)
        ActiveChart.FullSeriesCollection(i).Points(2).DataLabel.Select
        Selection.Delete  ' Delete second DataLabel; only want one per series
        ActiveChart.FullSeriesCollection(i).Points(1).DataLabel.Select
        Selection.Format.TextFrame2.TextRange.Font.Size = 12
        If i > 5 Then
            Selection.Left = 300
            Selection.Top = 100 + 50 * (i - 5)
            Selection.Format.TextFrame2.TextRange.Characters.Text = CStr(Selection.Left) & ", " & CStr(Selection.Top)
        Else
            Selection.Left = 100
            Selection.Top = 100 + 50 * i
            Selection.Format.TextFrame2.TextRange.Characters.Text = CStr(Selection.Left) & ", " & CStr(Selection.Top)
        End If
    Next
End Sub