Scalable Text Position by Scaling its Parent (QVtkRenderWindowInteractor) size vtk python

I have a render window that contains a text actor .
its widget container can scale and resize by user but the text position is still fixed.(I used grid layout with pyqt5 that is resizable and contains my render windows.)
I set the text on left-center and also want to be on left-center when the parent widget size become bigger or smaller.
How can I do this and make the text position scalable for all sizes and remain at the same position?
This is my code below :

   # Create Actor
    txtActor = vtk.vtkTextActor()
    # Set coordinates to match the old vtkScaledTextActor default value
    txtActor.SetDisplayPosition(x, y)
    # Set Text Properties
    txtprop = txtActor.GetTextProperty()
    txtprop.SetColor(1, .84, 0) 

and The output is :

regular size

bigger size
as you see in bigger size label ā€œLā€ is not center any more.