That's with a :height 0.9.  I think that looks visually less messy?

So we'd introduce a new face like this:

(defface fixed-pitch-for-proportional-buffers-but-a-better-name
  '((t :inherit fixed-pitch :height 0.9))
  "The basic fixed-pitch face."
  :group 'basic-faces)

And then use that in these primarily-proportional buffers.

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