subscript is set too low in math-mode with xits-math

Question

I use unicode-math with xits-math as math font and asana-math for math double-struck symbols. I compile with lualatex, and my packages are from TeXlive 2011.

Now, when use asana-math mixed with xits, I have the following problem:

In math mode, if I type $\deg_s ϕ$ my output is

What I want is:

Here is a minimal working example

\documentclass{minimal}

\usepackage{unicode-math}

    \setmathfont{xits-math.otf}
    \setmathfont[range={\mathbb}]{Asana-Math.otf}

\begin{document}
    $\deg_s \phi$
\end{document}

This problem also occurs when I use only asana-math as math font, so that's probably from where it comes. I need asana-math for its double-struck math characters which I prefer over xits-math's.

Is this a bug or is it supposed to be set so low? Can I fix this somehow? Is it unclean to mix fonts?

Edit: I now updated the question according to what I found out. Sorry for being so uninformative before, I underestimated the problem. : - ) (Thanks, Caramdir)

Answer 1

For some reason loading Asana Math changed the subscript shift drop parameter from 0.5pt to 2.22pt (probably the later value is derived from Asana Math).

You can see reset the value by setting \luatexUmathsubshiftdrop\textstyle=0.5pt, but it have to be called inside the formula, so you have to append it to the \everymath token:

\everymath=\expandafter{\the\everymath\luatexUmathsubshiftdrop\textstyle=0.5pt}

You probably want to the the same for display math:

\everydisplay=\expandafter{\the\everydisplay\luatexUmathsubshiftdrop\displaystyle=0.5pt}

To keep the things compatible with XeTeX, use \ifluatex.

\documentclass{minimal}

\usepackage{ifluatex}
\usepackage{unicode-math}

\setmathfont{xits-math.otf}
\setmathfont[range={\mathbb}]{Asana-Math.otf}

\ifluatex
  \everymath=\expandafter{%
    \the\everymath%
    \luatexUmathsubshiftdrop\textstyle=0.5pt}
  \everydisplay=\expandafter{%
    \the\everydisplay%
    \luatexUmathsubshiftdrop\displaystyle=0.5pt}
\fi

\begin{document}
  $\deg_s \phi_s$
\end{document}