FYI, the Font Height Options feature in Adobe Illustrator was recently added just a few weeks ago with the ".3" update of Illustrator CC 2020. I wish the font height options thing was always visible, but it does seem to be "sticky" once it is made visible in a document pre-set.
There are "purists" who insist type should never be manipulated in terms of physical letter height. These (mostly) are people who are used to setting type for print publication where the only thing which matters is how many points of distance is between one baseline to the next -usually on a layout grid. The default behavior (hiding the options) is there to make those people happy, IMHO.
Anyone wanting to set lettering according to cap height (or x-height) in literal physical sizes, like inches of height, in Adobe Illustrator must also be sure to change the measuring units for type to the same units used for the page, such as inches.
The "old" behavior in Adobe Illustrator (the blue box surrounding the text objects) was annoying. Doing any literal sizes of lettering, which would be applied to that bounding box was completely pointless. And that "Em Box" had no consistent relation to the font's actual UPM box and other dimensions.
shoresigns said:
That is possible, and I have heard of applications that determine metrics by measuring certain glyphs, but in most cases it's a stupid way to get vertical metrics, since all fonts have vertical metrics defined in the font file. Perhaps the app developers found it easier to measure an "H" than to learn how to read the vertical metrics.
All fonts have dimensions that define the position of the baseline, cap height, x-height, ascender and descender as it relates to the overall UPM square. Very few fonts are identical in these dimensions. I think the sign making apps (and Adobe Illustrator) use some kind of happy medium between looking at the font's built in dimensions and measuring glyphs between the baseline and physical tops of letters. That's because some fonts have their cap height lines set substantially above the tops of letters. In some cases it's way above.
For example, open Bickham Script Pro in a font editor like FontLab Studio and then open a glyph like the capital A. You'll see the ascender, cap height and x-height lines all set way above the glyph (at 680, 750 and 638 respectively). The literal top of the A is only about 428 units above the zero/baseline. 428 to 750 is a huge gap between the top of the letter and its defined cap height line. But in Adobe Illustrator when I set lettering in Bickham Script Pro Bold at 2" tall the top of that same capital letter A slightly over-shoots a 2" tall box snapped to the letter's baseline.
At least Adobe Illustrator will keep the letter height consistent if you change the typeface. The cap height will still be the same or logically close to it depending on the kind of typeface chosen. The cap heights stay exactly the same when switching from one geometrical sans face to another. When type is set in points using the normal page layout methods of physical sizes of the letters are often different when set in the same point size.