Lock Cells based on Dynamic Drop Down

[DavidG007]

Just after a bit of help if possible;

I have a workbook that has dynamic drop downs and works fine, however, I need to lock the cells that are not relevant based on set criteria. Attached pic to hopefully explain better.

I am using the vb code below for lock/unlock, again, works fine but does not interact with the drop down selection and range is not dynamic.

Private Sub Worksheet_Change(ByVal Target As Range)
    If Range("B4") = "Expansion" Then
        Range("F4:H4").Locked = False
    ElseIf Range("B4") = "SIB" Then
        Range("C4:E4").Locked = True
    End If
End Sub

Huge thanks for any feedback