Fretboard Diagrams and Capo's

I have a query as to why in the Fretboard Diagram I can’t I put a Capo on the “G” note and the dot on the “E” 6th string disappears. I would understand if the index-finger was being used as the barre, but it is the capo being used. Therefore, in my mind the shape of the “G” note should remain the same even with the capo on. How do I solve this?