RE: Making windows have same number of columns

[Drew Adams <drew.adams@oracle.com>]

> Changing the font size with text-scale-adjust has no affect on
> window-body-width; you can only change that by using
> shrink-window-horizontally or enlarge-window-horizontally if your frame
> has two or more side-by-side windows, or else if you change the width
> of the frame.

This doesn't directly address the original question, but FWIW:

Library `face-remap+.el' makes the `text-scale-*'
functions respect this new user option:

,----
| text-scale-resize-window is a variable defined in `face-remap+.el'.
| Its value is t
| 
| Documentation:
| Non-nil means text scaling resizes the window or frame accordingly.
| For example, if you use `C-x C--' (`text-scale-decrease')' to make the
| text smaller, then the window or frame is made smaller by a similar
| factor.
| 
| If the window is not alone in its frame, then the window is resized.
| Otherwise, the frame is resized (provided you also use library
| `fit-frame.el').  The frame is always resized both horizontally and
| vertically.
| 
| You can customize this variable. 
`----

One aim behind this is to not waste horizontal
whitespace in the window when you reduce the
displayed text size.

You can likely use similar code to get the
requested effect.

https://www.emacswiki.org/emacs/download/face-remap%2b.el