using the shorttitle field in a cross-referenced entry

Question

I'm using shorttitle in a bibliographic entry involved in crossreference. I'd like to display the shorttitle field when the parent entry is already called.

I have to use ext-verbose-trad2 style and memoir class.

Here an example code:

\documentclass[12pt, a4paper, openright, oneside]{memoir}
\usepackage{babel}
\usepackage[style=ext-verbose-trad2]{biblatex}
\begin{filecontents}[overwrite]{\jobname.bib}
@inbook{2018_Flor_NatchZhizn,
    crossref = {2018_Flor_BogosTrud},
    pages = {515-518},
    title = {Title of the beautiful composition}
}
@book{2018_Flor_BogosTrud,
    author = {Gualtieroni, P.},
    editor = {Brambilla, G.},
    publisher = {Florenziana},
    title = {Lavori teosofici 1902--1909},
    shorttitle = {LT.1902--1909},
    year = {2018}
}
\end{filecontents}
\addbibresource{\jobname.bib}
\begin{document}
\cite{2018_Flor_BogosTrud}\par
\cite{2018_Flor_NatchZhizn}
\end{document}

giving

should give for the second entry

Note: A similar problem is discussed here, but the example code contains a lot of complications and I cannot understand the answer.