The index spacing is somewhat problematic in STIX Two Math (v2.1) font. It is most evident with the root index, but subscripts are a little to close to the main symbol in my opinion, too. Exponents feel that way, as well. But especially those root indices...
Is there a way to improve it by a setting while loading the font or by other means?
A minimal working example:
% !TeX program = lualatex
\documentclass{article}
\usepackage{fontspec}
\usepackage{unicode-math}
\setmathfont{STIX Two Math}
\begin{document}
\( \sqrt[q]{a^p} P_k\)
\end{document}