The only way to enlarge an undersize picture is to do so manually or via a macro; there is no mailmerge setting to do this for you. Such a macro might be coded along the lines of:
Code:
Sub Demo()
Application.ScreenUpdating = False
Dim iShp As InlineShape
For Each iShp In ActiveDocument.InlineShapes
With iShp
.LockAspectRatio = True
If .Range.Information(wdWithInTable) = True Then
If .Range.Cells(1).PreferredWidthType = wdPreferredWidthPoints Then
.Width = .Range.Cells(1).Width
If .Range.Cells(1).HeightRule = wdRowHeightExactly Then
If .Height > .Range.Cells(1).Height Then
.Height = .Range.Cells(1).Height
End If
End If
End If
End If
End With
Next
Application.ScreenUpdating = True
End Sub
and would be run on the mailmerge output document.
For PC macro installation & usage instructions, see:
http://www.gmayor.com/installing_macro.htm
For Mac macro installation & usage instructions, see:
https://wordmvp.com/Mac/InstallMacro.html