Automated positioning of UserForm before UserForm.Show

I use an extension monitor, and my userForms sometime appear in odd places on the screens.
The following code places user form 'thisFrm' over the Application window:

    With thisFrm
        .StartUpPosition = 0
        .left = Application.left + (0.5 * Application.Width) - (0.5 * .Width)
        .top = Application.top + (0.5 * Application.height) - (0.5 * .height)
        .Show
    End With

I tried to automate the positions of several forms, and ran into problems below...

The line:     Debug.print "thisFrm.name = "; thisFrm.name         gave an Error. I find thisFrm IS Nothing
When the lines (below) followed by '**' were commented out, no errors occurred, and  MsgBox "WEEE" displayed (so the sub was run).

sub call1()
   Call userForm_Position("thisFrm")
end sub

Sub userForm_Position(formName As String)
    Dim frm As Object
    Dim thisFrm As Object
   
    For Each frm In VBA.UserForms
        If frm.name = formName Then  **
            Set thisFrm = frm  **
            exit sub  **
        End If  **
    Next
    Debug.print "thisFrm.name = "; thisFrm.name  **
    MsgBox "WEEE"
 
    With thisFrm  **
        .StartUpPosition = 0  **
        .left = Application.left + (0.5 * Application.Width) - (0.5 * .Width)  **
        .top = Application.top + (0.5 * Application.height) - (0.5 * .height)  **
        .Show  **
    End With  **

Is the enumeration   'Each frm In VBA.UserForms'   appropriate for forms that are not yet displayed ?
Ought the enumeration come from form objects specified in the VBE?

Floundering here!
Thanks
Kelvin