Excess whitespace around edges with distance style attribute

Question

When using the distance style attribute on edges, for example,

\tikzstyle{flowloop} = [out=-150, in=-30, looseness=0.8, loop, distance=7*\limw]

or

\tikzstyle{flowloop} = [out=-150,in=-30,looseness=0.8,distance=9*\limw]

I get excessive whitespace around my edges. I've tried using clip and 'use as bounding box' to no avail. Any suggestions on how to remove it or not have it appear in the first place? I've had to resort to using the 'pdfcrop' bundled with TeXLive to get rid of it.

See attached code and graphic to see what I mean. You'll notice that there's a loop's width of whitespace to the left and right of my two bottom loops.

\def\limw{0.050\textwidth}
\setlength{\tabcolsep}{1pt}
\renewcommand{\arraystretch}{0.3}
\def\bug{\includegraphics[width=\limw]{graphics/icons/kbugbuster}}
\def\suser{\includegraphics[width=\limw]{graphics/icons/system-users}}
\def\hat{\includegraphics[width=\limw]{graphics/icons/applications-engineering}}
\def\patch{\includegraphics[width=\limw]{graphics/icons/text-x-patch}}
\def\source{\includegraphics[width=\limw]{graphics/icons/text-x-objchdr}}
\def\debf{\includegraphics[width=\limw]{graphics/icons/application-x-deb}}
\def\litim{%
  \bug
  \hat
  \suser
  \patch
  \source
  }
\def\litimt{%
  \begin{tabular}{c c}
    \bug & \hat \\
    \suser & \patch\\
    \source &
  \end{tabular}
  }
\def\litimp{%
  \begin{tabular}{c c}
    \bug & \hat\\
    \suser & \patch\\
    \source & \debf
  \end{tabular}
  }
% Define a few styles and constants
\def\blockdist{8.0*\limw}
\def\logosize{3.2em}
\tikzstyle{projects} = [draw, fill=orange!30, text width=5em,
    text centered, minimum height=\logosize+0.6em,
    node distance=0.5*\blockdist and \blockdist]
\tikzstyle{ecosystem} = [projects, text width=6em, fill=blue!30,
    minimum height=12em, rounded corners, draw=black,dashed,
    node distance=\blockdist and \blockdist]
\tikzstyle{label} = [text width=6em, text centered,
    node distance=0.1*\blockdist and 0.1*\blockdist]
%\tikzstyle{flowloop} = [out=-150, in=-30, looseness=0.8, loop, distance=7*\limw]
\tikzstyle{flowloop} = [out=-150, in=-30,looseness=0.8,distance=9*\limw]%distance=8*\limw]
\pgfdeclarelayer{background2}
\pgfdeclarelayer{background1}
\pgfdeclarelayer{foreground}
\pgfsetlayers{background2,background1,main,foreground}

\begin{tikzpicture}
    \node (debian) [projects] {\includegraphics[height=\logosize]{graphics/logos/DebianLogo}};
    \node (derivs) [projects, node distance=5*\limw, below=of debian] {Debian derivatives};
    \node (decos label) [label,below=of derivs] {Debian ecosystem};

    \node (kde) [projects, above=of debian]
      {\includegraphics[height=\logosize]{graphics/logos/KDELogo}};
    \node(gcc) [projects, right=of kde]
      {\includegraphics[height=\logosize]{graphics/logos/GCCLogo}};
    \path ($ (kde)!.5!(gcc) $) node (upstr label) [label] {Upstream projects};

    \node (fedora) [projects, right=of debian]
      {\includegraphics[height=\logosize]{graphics/logos/FedoraLogo}};
    \node (OpenBSD) [projects, right=of derivs]
      {\includegraphics[height=\logosize]{graphics/logos/GentooLogo}};
    \node (oecos label) [label,below=of OpenBSD] {Other ecosystems};

    \begin{pgfonlayer}{background1}
      \node (oecos) [ecosystem, fit={(fedora) (OpenBSD) (oecos label)}] {};
      \node (decos) [ecosystem, fit={(decos label) (debian) (derivs)}] { };
    \end{pgfonlayer}

    \path ($ (oecos.south)!.5!(decos.south) $)+(0,-3em) node [label] (FOSS label) {FOSS Ecosystem};

    \begin{pgfonlayer}{background1}
    \end{pgfonlayer}


    \begin{pgfonlayer}{background1}
      \node (upstreams) [ecosystem,fit={(kde) (upstr label) (gcc)},minimum
      height=4em] {};
    \end{pgfonlayer}

    \path [draw, <->] (debian) -- node {\litimp} (derivs);
    \path [draw, <->] (decos.east) -- node[above] {\litim} (oecos.west);
    \path [draw, <->] (decos.north |- upstreams.south) -- node {\litimt} (decos.north);
    \path [draw, <->] (oecos.north |- upstreams.south) -- node {\litimt} (oecos.north);

    \path [draw, ->] (decos.270) edge[flowloop]
      node [pos=0.25] (lbugl) {\bug}
      node [pos=0.35] {\hat}
      node [pos=0.45] {\suser}
      node [pos=0.55] (lpatch) {\patch}
      node [pos=0.65] {\source}
      node [pos=0.75] {\debf}
      (decos.270);
    \path [draw, ->] (oecos.270) edge[flowloop]
      node [pos=0.25] {\bug}
      node [pos=0.375] {\hat}
      node [pos=0.50] {\suser}
      node [pos=0.625] (lpatch) {\patch}
      node [pos=0.75] (lsource) {\source}
      (oecos.270);
    \path [draw, ->] (upstreams.270) edge[flowloop]
      node [pos=0.25] {\bug}
      node [pos=0.375] {\hat}
      node [pos=0.50] {\suser}
      node [pos=0.625] {\patch}
      node [pos=0.75] {\source}
      (upstreams.270);

    \begin{pgfonlayer}{background2}
      \path[use as bounding box,clip] node (foss)
      [ecosystem,fill=blue!50,fit=(oecos) (decos) (lpatch) (lbugl) (lsource)
        (FOSS label) (upstreams)] {};
    \end{pgfonlayer}
    \clip (foss.north east) rectangle (foss.south west);
\end{tikzpicture}

See the following image to get an idea of the whitespace:

Answer 1

If you add the overlay option to your picture, the bounding box will be set to 0x0, which gets rid of the whitespace. You can prove it to yourself by putting the picture in an \fbox:

\fbox{\begin{tikzpicture}[overlay]
...
\end{tikzpicture}}

To re-establish the bounding box, I think the "use as bounding box" option on a path will do it.