When using more than one mathematical accent on top of a symbol inside \left[ \right], the symbol appears in the vertical centre of the brackets, leaving an empty space in the lower part of the symbol. Here is a MWE
\documentclass{article}
\usepackage{bm}
\newcommand{\sub}[1]{{\scriptscriptstyle\mathrm{#1}}} %Small Math Sub
\newcommand{\Cov}[1]{\mathrm{Cov}\left[#1\right]}
\begin{document}
$\left[\vec{\bm{s}}_\sub{n}\right]$
$\left[\hat{\vec{\bm{s}}}_\sub{n}\right]$
$\Cov{\vec{\bm{s}}_\sub{n}}$
$\Cov{\hat{\vec{\bm{s}}}_\sub{n}}$
$\Cov{\tilde{\bm{A}}_\sub{L_\sub{n}}}$
\end{document}
This extra space is a problem e.g. when inserting a math expression inline with text.
How can one remove the vertical empty space under the symbol so that the lower end of the brackets are aligned with it?