How to modify string height while keeping the face?

Question

Here's a code that works for setting a string foreground:

(defface test-face
  '((t (:height 1.2 :foreground "green")))
  "doc.")
(setq asdf (propertize "asdf" 'face 'test-face))
(add-face-text-property 0 (length asdf) '(:foreground "red") nil asdf)

asdf will still have the height 1.2 through test-face while gaining a red foreground, instead of green.

But this doesn't work:

(add-face-text-property 0 (length asdf) '(:height 1.0) nil asdf)

While the text properties will change, when inserting asdf into a fundamental-mode buffer, it will still have the height 1.2. How can I set the height to 1.0, while preserving the face?

Answer 1

Turns out the text height stacks the modifiers, so this works:

(add-face-text-property
 0 (length asdf)
 `(:height ,(/ 1 1.2)) nil asdf)