When I use package floatrow, option skip of package caption doesn't work

Question

Using this piece of code, I define a demo figure and its caption,

\documentclass{book}

\usepackage{graphicx}
\usepackage{caption}
    \captionsetup{
        }

\begin{document}
    \begin{figure}
        \includegraphics{example-image-a}
        \caption{Caption goes here.}
    \end{figure}
\end{document}

Now, according to Axel Sommerfeldt (here), I try to align caption with left side of figure. So, after modifying the above code, I write,

\documentclass{book}

\usepackage{graphicx}
\usepackage{floatrow}
\usepackage{caption}
    \captionsetup{
        slc=false
        }

\begin{document}
    \begin{figure}
        \ffigbox[\FBwidth]
        {\caption{Caption goes here.}}
        {\includegraphics{example-image-a}}
    \end{figure}
\end{document}

And the output is pretty well. But I like to adjust the space between the figure and its caption. As the document of package caption says, option skip does it,

\documentclass{book}

\usepackage{graphicx}
\usepackage{floatrow}
\usepackage{caption}
    \captionsetup{
        slc=false,
        skip=2cm
        }

\begin{document}
    \begin{figure}
        \ffigbox[\FBwidth]
        {\caption{Caption goes here.}}
        {\includegraphics{example-image-a}}
    \end{figure}
\end{document}

Unfortunately option skip makes no difference, unless I don't use package floatrow. What is the problem cause? Something like incompatibility? Is there any solution?

Answer 1

Use \floatsetup{captionskip=…}:

\documentclass{book}

\usepackage{graphicx}
\usepackage{floatrow}
\usepackage{caption}
    \captionsetup{
 slc=false,
 }

\begin{document}
    \begin{figure}
\floatsetup{captionskip=2cm}
        \ffigbox[\FBwidth]
        {\caption{Caption goes here.}}
        {\includegraphics{example-image-a}}
    \end{figure}
\end{document}