How can I scale mono font to 90% of MatchLowercase

\documentclass[12pt]{article}
\usepackage{fontspec}
\setmainfont{Source Serif Pro}[Scale=0.86] %=0.94*0.9
% Want 0.9 * MatchLowercase here:
\setmonofont{Latin Modern Mono}[Scale=MatchLowercase]

\setmainfont{Source Serif Pro}[Scale=0.94]
\setsansfont{Source Sans Pro}[Scale=MatchLowercase]
\newcommand\fox{The quick brown fox jumps over the lazy dog.}
\begin{document}
\fox\par
\textsf{\fox}\par
\texttt{\fox}\par
\end{document}

I've gotten a good year of use of Ulrike's answer (thank you!), but there is now a better way. Or maybe it was always there and I never noticed it. In any case, this is a straight-forward way of doing it with fontspec's ScaleAgain facility:

\setmonofont{Latin Modern Mono}[
  Scale       = MatchLowercase ,
  ScaleAgain  = 0.9 ,
  ]