Making buffer with same text scaling

This makes a frame and a buffer.  To have the new frame buffer=20
with the same text height, I apply `text-scale-mode-amount'
from the old to the new.  Yet when the old in +4, the new buffer=20
is +3.

(defun galaxiakos-du (frm-name bfr-name &rest implfds)
  "Call multiple implanted functions passed as arguments.
This allows dynamic insertion within the buffer.

FRM-NAME   Name for the frame.
BFR-NAME   Name for the buffer.
IMPLFDS    Implanted feed functions."
 =20
  (interactive)

  (let* ( (frame-inherited-parameters '(width height))
=09  (frm    (make-frame galaxiakos-frame-prmt))
          (bfr    (get-buffer-create bfr-name))
          (scale  text-scale-mode-amount) )

    ;; Change frame parameter for name
    (set-frame-parameter frm 'name frm-name)

    ;; Iterate and call each function passed as argument
    (select-frame frm)
    (with-current-buffer bfr
      (dolist (implfd implfds)
        (funcall implfd))
      (goto-char (point-min)))

    ;; Display the buffer in the selected frame
    (switch-to-buffer bfr)

    ;; Adjust step for scaling the text height
    (setq text-scale-mode-amount scale) ))