PGFplots with fillbetween and standalone class

Question

I am trying to produce a picture showing the mean value theorem for definite integrals. To do this I am using pgfplots with fillbetween. However, when using the standalone class I get a lot of blank space in the produced pdf file that shouldn't be there.

MWE:

\RequirePackage{luatex85}
\documentclass{standalone}
\usepackage{ifluatex}
\ifluatex
  \usepackage{fontspec}
  \setmainfont{Calibri}
  \usepackage{unicode-math}
  \setmathfont{Cambria Math}
\else
  \usepackage[utf8]{inputenc}
\fi

\usepackage{pgfplots}
\usepgfplotslibrary{fillbetween}

\begin{document}
\begin{tikzpicture}[scale=1.5]
  \begin{axis}[axis equal image,%
    axis lines=middle,%
    axis line style=thick,%
    clip=false,%
    xmin=0,%
    xmax=4,%
    ymin=0,%
    ymax=2.5,%
    every axis x label/.style={
      at={(ticklabel* cs:1.025)},
      anchor=west,
    },%
    every axis y label/.style={
      at={(ticklabel* cs:1.025)},
      anchor=south,
    },%
    xlabel=$x$,%
    ylabel=$y$,%
    ticks=none,%
    axis line style={->}]
    \addplot[thick,samples=200,domain=1:1.7436,name path=fEn]
      (x,{(x-2)*cos(3*pi*deg(x)/5) + 1});
    \addplot[thick,name path=cEn] coordinates {
      (1,1.2537) (1.7436,1.2537)};
    \addplot+[thick,fill=green!20] fill between [of=fEn and cEn];

    \addplot[thick,samples=200,domain=1.7436:2.6975,name path=fTo]
      (x,{(x-2)*cos(3*pi*deg(x)/5) + 1});
    \addplot[thick,name path=cTo] coordinates {
      (1.7436,1.2537) (2.6975,1.2537)};
    \addplot+[thick,fill=red!20] fill between [of=fTo and cTo];

    \addplot[thick,samples=200,domain=2.6975:3,name path=fTre]
      (x,{(x-2)*cos(3*pi*deg(x)/5) + 1});
    \addplot[thick,name path=cTre] coordinates {
      (2.6975,1.2537) (3,1.2537)};
    \addplot+[thick,fill=green!20] fill between [of=fTre and cTre];

    \addplot[thick,samples=200,domain=1:3]
      (x,{(x-2)*cos(3*pi*deg(x)/5) + 1}) node[near
      start,yshift=0.75cm,xshift=-0.125cm]{$y = f(x)$};
    \addplot[thick,densely dashed,domain=0:1.2537] (1.7436,1.2537 - x)
      node[below]{$c$};
    \addplot[thick] coordinates {
      (1,1.2537) (3,1.2537)};
    \addplot[thick,densely dashed,domain=0:1.309] (1,1.309 - x)
      node[below]{$a$};
    \addplot[thick,densely dashed,domain=0:1.809] (3,1.809 - x)
      node[below]{$b$};
  \end{axis}
\end{tikzpicture}
\end{document}

Any thoughts?