How to set \parindent for side heading?

Question

I am making tables with NiceTabular environment from nicematrix package and S-type columns from siunitx package. These tables have multi-line side headings. In accordance with guidelines for tables composition numbers must be centered vertically in cells or aligned bottom (A. Wolański, Edycja Tekstów):

It is done with the use of m-type column for side heading, which was suggested by @Werner here. Moreover in the case of multiline cells in side heading it is necessary to indent all lines with exception for the first line:

How to modify the code to get this effect? I tried apply the solution given here, but without success. How to force the text in the m-type column to be left-justified?

Code:

\documentclass{standalone}
\usepackage{nicematrix}         % for NiceTabular environment
\usepackage{siunitx}            % for proper horizontal alignments of numbers
\usepackage{booktabs}       % for commands \toprule, \midrule, \bottomrule
\begin{document}
\begin{NiceTabular}{
    >{\setlength{\parindent}{-1em}}m{2cm}
    S[table-format=2.2]
    S[table-format=3.1]
}
    \toprule
    \multicolumn{1}{c}{First descr.} & \multicolumn{1}{c}{Second descr.} & \multicolumn{1}{c}{Third descr.}\
    \midrule
    Long first side heading & 1.1 & 11.1\
    Also long second side heading & 11.11 & 111.1\
    \bottomrule
\end{NiceTabular}
\end{document}

Answer 1

Using @Fran comment and the answer concerning ragged right text in the cell I got:

\documentclass{standalone}
\usepackage{nicematrix}      % for NiceTabular environment
\usepackage{siunitx}         % for proper horizontal alignments of numbers
\usepackage{booktabs}        % for commands \toprule, \midrule, \bottomrule
\usepackage{ragged2e}        % for ragged right text
\begin{document}
\begin{NiceTabular}{
    >{\RaggedRight\arraybackslash\hangindent1em}m{3.5cm}
    S[table-format=2.2]
    S[table-format=3.1]
}
    \toprule
    \multicolumn{1}{c}{First descr.} & \multicolumn{1}{c}{Second descr.} & \multicolumn{1}{c}{Third descr.}\
    \midrule
    Long text in the first side heading cell & 1.1 & 11.1\
    Also long text in the second side heading cell & 11.11 & 111.1\
    \bottomrule
\end{NiceTabular}
\end{document}