[Tex/LaTex] Beamer: Full width image, aligned to top with a frame title

Question

I would like to include a full width image, aligned to the top of a frame with a frame title. The problem is, I cannot get rid of a line of white space between the orange frame title header and the lion image.

\documentclass[t]{beamer}
% Frames are 128x96mm and top-aligned by default.

% Calculate with \sidebarwidth
\usepackage{calc}
\newlength{\sidebarwidth}

% Theme
\setlength{\sidebarwidth}{28mm}
\usetheme[height=16mm, right, width=\sidebarwidth]{Goettingen}
% Hence, a full frame image is 100x80mm
\usecolortheme{crane}

% Include full-width graphics
\usepackage{graphicx}
\newcommand{\includefullwidthgx}[2][]{%
\noindent\makebox[\columnwidth]{\includegraphics[width=128mm-\sidebarwidth, #1]{#2}}%
}%

\begin{document}
\begin{frame}
\frametitle{frame title text}
\includefullwidthgx{lion.jpg}
\end{frame}
\end{document}

Answer 1

I helped myself out by adding a \vspace{-9.5pt}. The value seems not to change with standard themes. Nor does it matter whether a subtitle is present in the header. Still, I find it a non-general, somewhat sub-optimal solution. Who does better?

\documentclass[t]{beamer}
% Frames are 128x96mm and top-aligned by default.

% Calculate with \sidebarwidth etc.
\usepackage{calc}
\newlength{\sidebarwidth}

% Theme
\setlength{\sidebarwidth}{28mm}
\usetheme[height=16mm, right, width=\sidebarwidth]{Goettingen}
% Hence, a full frame image is 100x80mm
\usecolortheme{crane}

% Include full-width graphics
\usepackage{graphicx}
\newcommand{\includefullwidthgx}[2][]{%
\vspace{-9.5pt}
\noindent\makebox[\columnwidth]{\includegraphics[width=128mm-\sidebarwidth, #1]{#2}}%
}%

\begin{document}
\begin{frame}
\frametitle{Sub-optimal solution.}
\framesubtitle{Anyone does better?}
\includefullwidthgx{lion.jpg}
\end{frame}

\end{document}