Epigraph Package: flushepinormal option, and the vertical space between the epigraph and the source in general

Question

Below is the epigraph package with and without flushepinormal option.

\documentclass[12pt]{article}
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
\usepackage[T1]{fontenc}
\usepackage[utf8]{inputenc}
\usepackage[american]{babel}
\usepackage{microtype}
\usepackage{libertine}
\usepackage{epigraph}
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
\setlength{\epigraphrule}{0pt}
\setlength{\epigraphwidth}{1\textwidth}
% \renewcommand{\textflush}{flushepinormal}
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
\begin{document}
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
\epigraph{To be clever enough to get all that money, one must be stupid enough to want it.}{G.K. Chesterton}
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
\end{document}
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

\documentclass[12pt]{article}
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
\usepackage[T1]{fontenc}
\usepackage[utf8]{inputenc}
\usepackage[american]{babel}
\usepackage{microtype}
\usepackage{libertine}
\usepackage{epigraph}
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
\setlength{\epigraphrule}{0pt}
\setlength{\epigraphwidth}{1\textwidth}
\renewcommand{\textflush}{flushepinormal}
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
\begin{document}
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
\epigraph{To be clever enough to get all that money, one must be stupid enough to want it.}{G.K. Chesterton}
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
\end{document}
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

1. Is it possible to apply flushepinormal without causing the extra vertical spacing?
2. In general, is it possible to control the vertical spacing between the epigraph and the source?

Answer 1

The code below (to be put into the preamble after \usepackage{epigraph}) adds an optional parameter to the \epigraph command that can be used to control the distance between text and its source locally for one epigraph.

\epigraph[extra space between text and source]{text}{source}

Moreover, there is a parameter \interepigraphskip to modify the space globally; originally it is zero.

\setlength\interepigraphskip{extra space between text and source}

This is the code that has to be added to the preamble:

\makeatletter
\newlength\interepigraphskip
\setlength\interepigraphskip{0ex}
\renewcommand\epigraph[3][\interepigraphskip]{\vspace{\beforeepigraphskip}
  {\epigraphsize\begin{\epigraphflush}\begin{minipage}{\epigraphwidth}
    \@epitext{#2}\\[#1] \@episource{#3}
    \end{minipage}\end{\epigraphflush}
    \vspace{\afterepigraphskip}}}
\makeatother

Here are some examples, including the problem of the original posting.

\documentclass[12pt]{article}
\addtolength\textheight{1cm} % Just to make the examples fit on one page
\usepackage{epigraph}
\makeatletter
\newlength\interepigraphskip
\setlength\interepigraphskip{0ex}
\renewcommand\epigraph[3][\interepigraphskip]{\vspace{\beforeepigraphskip}
  {\epigraphsize\begin{\epigraphflush}\begin{minipage}{\epigraphwidth}
    \@epitext{#2}\\[#1] \@episource{#3}
    \end{minipage}\end{\epigraphflush}
    \vspace{\afterepigraphskip}}}
\makeatother
\begin{document}
\paragraph{No extra space:}
\epigraph{To be clever enough to get all that money, one must be stupid enough to want it.}{G.K. Chesterton}

\paragraph{Extra space of 3 ex, locally:}
\epigraph[3ex]{To be clever enough to get all that money, one must be stupid enough to want it.}{G.K. Chesterton}

\paragraph{Setting extra space to 5 ex, globally:}
\setlength\interepigraphskip{5ex}
\epigraph{To be clever enough to get all that money, one must be stupid enough to want it.}{G.K. Chesterton}
\setlength\interepigraphskip{0ex} % Setting parameter back for next examples

\paragraph{Original post, default:}  
\setlength{\epigraphrule}{0pt}
\setlength{\epigraphwidth}{1\textwidth}
\epigraph{To be clever enough to get all that money, one must be stupid enough to want it.}{G.K. Chesterton}

\paragraph{Original post, case flushepinormal:}  
\renewcommand{\textflush}{flushepinormal}
\epigraph{To be clever enough to get all that money, one must be stupid enough to want it.}{G.K. Chesterton}

\paragraph{Original post, case flushepinormal, space corrected:}  
\epigraph[-\baselineskip]{To be clever enough to get all that money, one must be stupid enough to want it.}{G.K. Chesterton}
\end{document}

Answer 2

Here is a solution to your first problem. In the case of epigraphflushnormalyou can control the spacing between text and source by changing the argument of \vspace*:

\documentclass[12pt]{article}
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
\usepackage[T1]{fontenc}
\usepackage[utf8]{inputenc}
\usepackage[american]{babel}
\usepackage{microtype}
\usepackage{libertine}
\usepackage{epigraph}
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
\setlength{\epigraphrule}{0pt}
\setlength{\epigraphwidth}{\textwidth}
 \renewcommand\textflush{flushepinormal}
 \renewenvironment{flushepinormal}{}{\vspace*{-\baselineskip}}
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
\begin{document}

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
\epigraph{To be clever enough to get all that money, one must be stupid enough to want it.}{G.K. Chesterton}

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
\end{document}