Fontspec, set font size for italic

Question

XeLaTeX

How can I set different font for all italic in the document?

\setromanfont[StylisticSet=2,
 ItalicFont={Phenomena Light},
{Cormorant Medium}  % Основной шрифт текста

It's work. But I can't set ItalicFont size

\setromanfont[StylisticSet=2,
    ItalicFont={Phenomena Light},
    ItalicFeatures={FontSize=11pt}]
    {Cormorant Medium}  % Основной шрифт текста

Don't work, get an error.

The size of the main text 12pt. The font for italics is slightly higher than the main text.

Answer 1

I would use the \defaultfontfeatures directive to match the x-heights of all fonts automatically. E.g.,

\documentclass{article}
\usepackage{fontspec}
\defaultfontfeatures{Scale=MatchLowercase}
\setmainfont[ItalicFont={Times New Roman Italic}]{Arial}

\begin{document}
The \textit{quick} brown \textit{fox} jumps \textit{over} the \textit{lazy} dog.
\end{document} 

where I've substituted in two fonts which happen to be available on my system. The result is:

For comparison, this is what one gets without the \defaultfontfeatures directive -- observe the vastly different x-heights of the main and italic font:

Answer 2

Use Scale. In the example I use Scale=2 just by way of example; you may want to use

Scale=MatchUppercase

or

Scale=MatchLowercase

instead of an explicit factor.

\documentclass{article}
\usepackage{fontspec}

\setmainfont{TeX Gyre Termes}[
  ItalicFont={TeX Gyre Heros Italic},
  ItalicFeatures={Scale=2},
]

\begin{document}

Upright text and \textit{italic}

\end{document}