Use \delimiterfactor with slash (xits)

Question

I am trying to slightly reduce the dimensions of the \slash delimiter with \delimiterfactor.

\documentclass[12pt]{article}
\usepackage{unicode-math}
\setmathfont{xits-math.otf}
\begin{document}

\newcommand{\hfrac}[2]{\left.#1\middle\fracslash#2\right.}
\[ a/b \qquad \hfrac{a}{b} \qquad \hfrac{\sqrt{3}}{3} \qquad x^{\hfrac{1}{2}} \qquad x^{y^{\hfrac{2}{3}}} \]

\renewcommand{\hfrac}[2]{\delimiterfactor=850\left.#1\middle\fracslash#2\right.}
\[ a/b \qquad \hfrac{a}{b} \qquad \hfrac{\sqrt{3}}{3} \qquad x^{\hfrac{1}{2}} \qquad x^{y^{\hfrac{2}{3}}} \]

\renewcommand{\hfrac}[2]{\delimiterfactor=800\left.#1\middle\fracslash#2\right.}
\[ a/b \qquad \hfrac{a}{b} \qquad \hfrac{\sqrt{3}}{3} \qquad x^{\hfrac{1}{2}} \qquad x^{y^{\hfrac{2}{3}}} \]

\end{document}

Here is the result.

Switching from 901 (default value) to 850 as no effect but switching to 800 get an huge reduction (it also looks like the delimiter is slightly too shifted down). How can I get something more smooth ? (the \delimitershortfall command seems not helping)

Answer 1

Since slash is only available in some fixed sizes (thx @egreg), the following solution using scalerel is not bad.

\documentclass[12pt]{article}
\usepackage{unicode-math}
\setmathfont{xits-math.otf}
\usepackage{scalerel}
\newcommand{\hfrac}[2]{#1\scalerel{\divslash}{\vphantom{#1}#2}}
\begin{document}

\[ \hfrac{a}{b} \qquad \hfrac{\sqrt{a}}{(b+c)} \qquad \hfrac{1}{\sqrt{a}} \qquad x^{\hfrac{1}{2}} \]

\end{document}