Why the same font size for different latex sections with Auctex when `font-latex-fontify-sectioning` is a float?

Question

As far as I understand, setting font-latex-fontify-sectioning to a number larger than 1.0 should make it so that the titles of sections of different levels have different sizes.

However, even though I set this variable to 3.5 as in:

(setq font-latex-fontify-sectioning 3.5) ;; headers with larger font

This is still not working. Instead, their fonts have different colors, not different sizes, as if this variable was set to color.

Why am I getting the same font size?

---

EDIT/UPDATE:

Since I asked this question I managed to find the main issue: I had a hook activating TeX-fold-mode which seems to override the section face set by font-latex-fontify-sectioning. I also had a hook running outline-hide-body, but this does not seem to interfere with font-latex-fontify-secitoning.

If instead of running these with the hook I run this function interactively, all goes well:

(defun latex-activate-outline-and-hide-body ()
  (outline-minor-mode 1)
  (outline-hide-body) ;; fold all sections
)

(defun latex-activate-folding-and-hide-buffer ()
  (TeX-fold-mode 1)
  (TeX-fold-buffer) ;; fold envs and macros
)

(defun latex-neat-folding ()
  (interactive "@")
  (setq font-latex-fontify-sectioning 1.3)
  (font-latex-update-sectioning-faces)
  (latex-activate-outline-and-hide-body)
  (latex-activate-folding-and-hide-buffer)
)

Surprisingly enough (to me - probably due to my limited understanding of hooks), this does not work if I add this function to latex's hook:

(add-hook 'TeX-mode-hook 'latex-neat-folding)