I wanted to put the subscript below and above the box (shown in image), similar to how it happens for \sum. \displaystyle is not applicable. How can I make it placed there?
Here is my definition of the box:
\documentclass[12pt]{report}
\usepackage{amsmath,amsthm,amssymb,setspace}
\usepackage{scalerel}
\def\mcirc{\mathbin{\scalerel*{\bigcirc}{t}}}
\def\msquare{\mathord{\scalebox{1}[1]{\scalerel*{\Box}{\strut}}}}
\begin{document}
$\msquare_{i=1}^{k} C_{n_i}$
\end{document|


\underset,\oversetand/or\overundersetas mentioned here? – Lukas Jun 22 '22 at 09:12\mathordwith\mathop– egreg Jun 22 '22 at 10:12