VBA- If/Elseif statement for selecting a dynamic range in excel

I'm trying to use For/If/Else if to test criteria and return various ranges depending on whether certain cell are empty or not, then past that range into an email.

When I run the code below it only returns range B15:G20, no matter if the cell in question (b20) is empty or not. Ideally I'd like it to test up to 4 four cells to see if they're empty or not and return a range that only contains cells with data in them.

Sub EXPVendorCopyRangeToOutlook_single()
    'Declare Outlook Vairables
    Dim oLookApp As Outlook.Application
    Dim oLookItm As Outlook.MailItem
    Dim oLookIns As Outlook.Inspector
    
    'Declare Word Vaiables
    Dim oWrdDoc As Word.Document
    Dim oWrdRng As Word.Range
    
    'Declare Excel Variables
    Dim ExcRng As Range
    
    On Error Resume Next
    'Get the Active instance of Outlook
    Set oLookApp = GetObject(, "Outlook.Application")
    
    'If error create a new instance of outlook
    If Err.Number = 429 Then
        'Clear Error
        Err.Clear
        
        'Create new instance of Outlook
        Set oLookApp = New Outlook.Application
        
    End If
    'Create a new email 'Possible Problem here
    Set oLookItm = oLookApp.CreateItem(olMailItem)
    'Create a reference to the ex range you want to export
    
    For Each Cell In Worksheets("sheet1")
        If Not IsEmpty(b20.Value) Then
            Set ExcRng = Sheet1.Range("b15:g20")
        ElseIf Not IsEmpty(b19.Value) Then
            Set ExcRng = Sheet1.Range("b15:g18")
        End If
    Next
        
    With oLookItm
    
        'Define basic info
        .From = "ABC@XYZ.COM"
        
        .To = "123@345.COM"
        .CC = ""
        .Subject = Range("m3")
        
        .Body = "Please review the attached invoices and confirm that the goods or services have been received and payment should be made."
        
        'Display email
        .Display
        'Get the active inspector
        Set oLookIns = .GetInspector
        
        'Get word editor
        Set oWrdDoc = oLookIns.WordEditor
        
        'Specify rang in document
        Set oWrdRng = oWrdDoc.Application.ActiveDocument.Content
            oWrdRng.Collapse Direction:=wdCollapseEnd
        
        'Add new paragraphand then insert break
        Set oWrdRng = oWdEditor.Paragraph.Add
            oWrdRng.InsertBreak
        
        'Copy the Range
        ExcRng.Copy
        
        'Paste it
        oWrdRng.PasteSpecial DataType:=wdPasteMetafilePicture
    End With
End Sub

This is the part of the code giving me problems.

For Each Cell In Worksheets("sheet1")
    If Not IsEmpty(b20.Value) Then
        Set ExcRng = Sheet1.Range("b15:g20")
    ElseIf Not IsEmpty(b19.Value) Then
        Set ExcRng = Sheet1.Range("b15:g18")
    End If
Next

I feel like i'm overlooking something simple with syntax...idk TIA