It would be a lot easier to resize the chart original in Excel. If the size is important, you may be able to duplicate the chart on a hidden worksheet in the same workbook where you can resize the chart and then use that version to paste into Word.

Assuming that you can't do that, the next easiest option would be to bookmark each of the graphics so you don't need to query the field code values. If this was done, the following code could be adapted to work.
Dim aPic As InlineShape
Set aPic = ActiveDocument.Bookmarks("Chart1").Range.InlineSha pes(1)
With aPic
.Width = 400
.Height = 200
End With