Setstretch Woes in Floats

Question

LaTeX is really not very user-centric when it comes to font-line spacing. Most users would expect the linespacing to change at the place where invoked. I have run into issues like this many times, and usually found hacks (uselessly changing font size, for example) to make it happen how it want it. But it would really be nice to learn how this really ought to be done correctly. So, here is the example that illustrates the question:

\documentclass[11pt]{article}
\usepackage{color}
\usepackage{setspace}
\setstretch{0.75}  %% at 10pt, min seems to be 0.75;  0.7 is more distant, 0.8 is more distant
\newcommand{\notesclass}[2]{{\par{\setstretch{5}\medskip\noindent\tiny\textbf{#1:} #2}}\par}
%% useless overkill: \renewcommand{\notesclass}[2]{\begin{minipage}{\textwidth}{\par{\setstretch{5}\medskip\noindent\tiny\textbf{#1:} #2}}\par\end{minipage}\par}
\providecommand{\source}[1]{\notesclass{Source}{#1}}
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
\begin{document}
I am trying to define a macro that reliably typesets content (that explains my tables) in a
font-size and line-spacing of my preference.
For sake of visual illustration, I have set the main text to ugly 0.75 spacing.  (I also do not 
understand why 0.75 is the minimum setstretch spacing when 10pt is my article main font; either 
0.7 or 0.8 creates linespacing that is larger.)
\begin{table}\color{blue}
--- Table Blue Starts
\source{I would have wanted the 5 spacing here.  Why does this still have spacing that seems 
to be based on the font-size of the main paragraph (10pt)?  LaTeX has recognized that it is in 
tiny.}
--- Table Blue Ends
\end{table}
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
\begin{table}\color{red}
--- Table Red Starts
\source{I understand why this has 5 spacing relative to the actual font size that I used. It 
is actually what I wanted.
Alas, despite the par at the end of the notesclass macro, this has the same normalsize-

font-related 0.75 separation that I did not want. I would have wanted the 5 spacing here.  Even 
stranger, if the documentclass is changed from 11pt to 12pt, table red changes in incongruous fashion.}
--- Table Red Ends
\end{table}
\end{document}

What comes out is

Of course, my intent is not to use 5.0 linespacing, but 0.95 linespacing on a footnotesize font in order to compactly display the source references for my floats.

Answer 1

Your code has \par in the wrong place: it should be before the closing brace limiting the scope of \tiny.

On the other hand, a space saving of 0.7pt over three lines doesn't seem worth the pain, but you're the final judge.

You don't need setspace for this application.

\documentclass[11pt]{article}
\usepackage{lipsum}
\newcommand{\notesclass}[2]{%
  \par\medskip
  {\linespread{0.95}\tiny\noindent\textbf{#1:} #2\par}%
}
\newcommand{\source}[1]{\notesclass{Source}{#1}}
\begin{document}
\source{\lipsum[1][1-4]}
As a comparison, the same with just \verb|\tiny|
\medskip{\tiny\noindent\textbf{Source:} \lipsum[1][1-4]\par}
\sbox0{\parbox[b]{\textwidth}{\source{\lipsum[1][1-4]}}}\the\ht0
\sbox0{\parbox[b]{\textwidth}{\medskip\tiny\noindent\textbf{Source:} \lipsum[1][1-4]}}\the\ht0
\end{document}