In an empty buffer, m-: of
(let ((p (point))) (insert " ") (add-text-properties p (point) `(display (space :width 7))) (insert ".") (current-column))
returns 2 in gui mode but 8 in character mode of emacsen more recent than emacs 22. (I tried it in several emacs versions including the most recent 27.0.50 snapshot.)
I discovered this by figuring out why the m-x bubbles game hasn't worked in character mode since emacs 22.