How can I afford both superscript and subscript in textmode, but with compressed incides? I have found the following approach to frist of all get both superscript and subscript in textmode: Superscript and subscript together in text mode
\documentclass{article}
\makeatletter
\DeclareRobustCommand{\textsupsub}[2]{{%
\m@th\ensuremath{%
^{\mbox{\fontsize\sf@size\z@#1}}%
_{\mbox{\fontsize\sf@size\z@#2}}%
}%
}}
\makeatother
\begin{document}
X\textsupsub{ab}{c}X\textsupsub{c}{ab}X
\end{document}
This works fine, but the indices are oddly big:

Whereas when I just use subscript for instance, the indices are kind of compressed to fit in the text around:

Does anyone know what to do or add to obtain a similar result regarding the incides to plain subscript oder superscript?
I have now added a MWE:
%Definition des Dokumentes
\documentclass[12pt,a4paper,twoside,openright]{report}
%Schriftart Arial - ACHTUNG: Compile with XeLaTeX (not PDFLaTeX)!
\usepackage{fontspec}
\defaultfontfeatures{Scale = MatchLowercase}
\setmainfont{Arial}[Scale = 1.0]
%Deutsche Umlaute, Englisch
\usepackage[main = ngerman, english]{babel}
%Mathematische Symbole und Zeichen
\usepackage{amsmath}
\usepackage{amssymb}
\usepackage{mathtools}
% = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = =
% Sonstige Makros
% = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = =
\makeatletter
\DeclareRobustCommand{\textsupsub}[2]{{%
\m@th\ensuremath{%
^{\mbox{\fontsize\sf@size\z@#1}}%
_{\mbox{\fontsize\sf@size\z@#2}}%
}%
}}
\makeatother
% = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = =
%
%
% Anfang von Dokumententext
%
%
% = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = =
\begin{document}
R\textsubscript{GT, b}
R\textsuperscript{*}
R\textsupsub{*}{GT, b}
\end{document}
It gives the following output:
I would like to have a mixture of the first two, but it generates too big indices.

\textsupsub? This looks like math to me. – egreg Feb 24 '20 at 22:12\textsupsubbecause I have to use Arial in my text and I didn't find a way to do so in equations hence math too. At least in the text I intend to use Arial for variables used in following equations. – TeXlearner Mar 06 '20 at 16:00