Inconsistent sorting results with transliteration

[moewew]

See also https://tex.stackexchange.com/q/718991/35864

\documentclass[12pt]{article}
\usepackage[backend=biber, style=authoryear-comp, sorting=nty]{biblatex}
\usepackage{libertinus-otf}

\DeclareSortTranslit{
  \translit[russian]{*}{russian}{bgn/pcgn-standard}%{setnames}
}

\begin{filecontents*}{\jobname.bib}
@book{2021_Flor_Trudy,
address = {Сергиев Посад},
author = {Флоренский, П. А.},
langid = {russian},
publisher = {Таисии},
title = {Философские труды},
year = {2021},
}
@book{2015_Flor_SullaSupEMiracolo, 
address = {Milano},
author = {Florenskiy, P. A.},
editor = {Valentini, Natalino},
publisher = {SE},
title = {Sulla superstizione e il miracolo},
year = {2015},
}
\end{filecontents*}
\addbibresource{\jobname.bib}

\begin{document}
Citing different authors \autocite{2015_Flor_SullaSupEMiracolo, 2021_Flor_Trudy}

\printbibliography
\end{document}

produces

For me, even though I expected the latter entry to sort before the former.

One issue I found is that with biber --debug I get

[478] Biber.pm:4390> DEBUG - 2015_Flor_SullaSupEMiracolo => mm,,Florenskiy P. A.   ,Sulla superstizione e il miracolo,2015,0
[478] Biber.pm:4390> DEBUG - 2021_Flor_Trudy => mm,,FlorenskiyP. A.   ,Filosofskiye trudy,2021,0

meaning that the sort key for the transliterated entry and the Latin entry differ subtly in the spacing before the give name bit. Presumably that is already enough for them to sort differently.