Originally Posted by derangedhermit
Smallcaps are the same height as the x-height. The x-height is the height of a lower case "x"....
X-height is a font metric, one of many, that is inside every opentype font file.
It can't be a % of cap height since the ratio x-height/cap-height varies....
Cap height is not necessarily the same as the value for 1em, either.
"Em" used to be a horizontal measurement - the width of a capital M.
Thanks a lot for stressing clearly these main points and commenting them. So, as far as height is concerned, we have better check visually after every font change.
It seems that, finally, after losing some time on it, I got some acceptable results for fake and true smallcaps.
To put them on equal footing, I choose a 92% font-size for the paragraph and then
- uppercase with 0.75em for the fake ('Serif' font)
- lowercase for the true ('Linux Libertine')
These values above could be further tweaked but I dare not.
From left to right: fake, true, printed.