beamer: content top and bottom margins

Question

It is trivial to modify the left and right margins in beamer.

But what about the top and bottom?

If possible, I would like to reduce a little bit that top margin, marked with the hand-drawn red arrow:

MWE:

\documentclass[t]{beamer}

\setbeamersize{text margin left=0.5em, text margin right=0.5em}
\setbeamertemplate{frametitle}{\color{black}\bfseries\insertframetitle\par\vskip-6pt\hrulefill}

\newcommand\FourQuad[4]{
    \colorbox{yellow}{\begin{minipage}[b][.40\textheight][t]{.49\textwidth}#1\end{minipage}}\hfill
    \begin{minipage}[b][.40\textheight][t]{.49\textwidth}#2\end{minipage}\\
    \begin{minipage}[b][.40\textheight][t]{.49\textwidth}#3\end{minipage}\hfill
    \begin{minipage}[b][.40\textheight][t]{.49\textwidth}#4\end{minipage}
}

\begin{document}

\begin{frame}
\frametitle{A frame divided in four quadrants}
\FourQuad%
{First quadrant contents and some more text text text text more text text text text more text text text text more text text text text more text text text text more text text text text more text text text text}%
{
  \centering
  \rule{3cm}{2cm}
  A test figure.
}%
{\begin{align*}
  a &= b \\
  &= c \\
  & = d.
\end{align*}}%
{Fourth quadrant contents and some more text text text text more text text text text more text text text text more text text text text more text text text text more text text text text more text text text text}
\end{frame}

\end{document}

Answer 1

Do you want to do this only for your "quad"-frame or globally? For only this special frame, a quick hack would be to simply insert \vspace{}

\documentclass[t]{beamer}

\setbeamersize{text margin left=0.5em, text margin right=0.5em}
\setbeamertemplate{frametitle}{\color{black}\bfseries\insertframetitle\par\vskip-6pt\hrulefill}

\newcommand\FourQuad[4]{
        \vspace*{-0.2cm}
    \colorbox{yellow}{\begin{minipage}[b][.40\textheight][t]{.49\textwidth}#1\end{minipage}}\hfill
    \begin{minipage}[b][.40\textheight][t]{.49\textwidth}#2\end{minipage}\\
    \begin{minipage}[b][.40\textheight][t]{.49\textwidth}#3\end{minipage}\hfill
    \begin{minipage}[b][.40\textheight][t]{.49\textwidth}#4\end{minipage}
}

\begin{document}

\begin{frame}
\frametitle{A frame divided in four quadrants}
\FourQuad%
{First quadrant contents and some more text text text text more text text text text more text text text text more text text text text more text text text text more text text text text more text text text text}%
{
  \centering
  \rule{3cm}{2cm}
  A test figure.
}%
{\begin{align*}
  a &= b \\
  &= c \\
  & = d.
\end{align*}}%
{Fourth quadrant contents and some more text text text text more text text text text more text text text text more text text text text more text text text text more text text text text more text text text text}
\end{frame}

\end{document}

---

EDIT:

To make this hack globally, add the \vspace{} to the frametitle template

\documentclass[t]{beamer}

\setbeamersize{text margin left=0.5em, text margin right=0.5em}
\setbeamertemplate{frametitle}{\color{black}\bfseries\insertframetitle\par\vskip-6pt\hrulefill \vspace*{-0.2cm}}

\newcommand\FourQuad[4]{
    \colorbox{yellow}{\begin{minipage}[b][.40\textheight][t]{.49\textwidth}#1\end{minipage}}\hfill
    \begin{minipage}[b][.40\textheight][t]{.49\textwidth}#2\end{minipage}\\
    \begin{minipage}[b][.40\textheight][t]{.49\textwidth}#3\end{minipage}\hfill
    \begin{minipage}[b][.40\textheight][t]{.49\textwidth}#4\end{minipage}
}

\begin{document}

\begin{frame}
\frametitle{A frame divided in four quadrants}
\FourQuad%
{First quadrant contents and some more text text text text more text text text text more text text text text more text text text text more text text text text more text text text text more text text text text}%
{
  \centering
  \rule{3cm}{2cm}
  A test figure.
}%
{\begin{align*}
  a &= b \\
  &= c \\
  & = d.
\end{align*}}%
{Fourth quadrant contents and some more text text text text more text text text text more text text text text more text text text text more text text text text more text text text text more text text text text}
\end{frame}

\end{document}