FWIW if you use the following to run the merge, you can include the macro at merge time, though if using Paul's macro it would require a minor change to be compatible (see below)
https://www.gmayor.com/MergeAndSplit.htm
Code:
Sub FixImages(oDoc As Document)
Application.ScreenUpdating = False
Dim Tbl As Table, iShp As InlineShape
For Each Tbl In oDoc.Tables
With Tbl.Range
For Each iShp In .InlineShapes
With iShp
.LockAspectRatio = True
With .Range.Cells(1)
If .Height <> iShp.Height Then
If .Width <> iShp.Width Then
iShp.Height = .Height
If iShp.Width > .Width Then
iShp.Width = .Width
End If
End If
End If
End With
End With
Next
End With
Next
End Sub