Code:
\documentclass[]{article}
\usepackage[ngerman]{babel}
\usepackage[T1]{fontenc}
\usepackage{amsmath}
\usepackage{xpatch}
\makeatletter
\newcommand\my@tag@fontsize{\normalsize}
\xpatchcmd\maketag@@@{\m@th}{\m@th\my@tag@fontsize}{}{\show\failed}
\let\amsmath@eqref\eqref
\renewcommand\eqref[1]{{\let\my@tag@fontsize\relax\amsmath@eqref{#1}}}
\makeatother
\begin{document}
\begin{align}
\mathcal{L}\label{A}
\end{align}
Zwischentext
\tiny
\begin{align}
\mathcal{D}\label{B}
\end{align}
\normalsize
Es geht weiter... \eqref{A}
\end{document}
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