How to set parindent for side heading?

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}

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}{
    >{RaggedRightarraybackslashhangindent1em}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}