Arrows over letter in LaTeX file indicating a ray is not drawn correctly

Question

I am adopting code for drawing arrows above letters indicating rays from Steven B. Segletes; he had replied to a post "Typesetting arrows above a pair of letters to indicate a line" on tex.stackexchange.com. When I changed the font to \footnotesize, the arrow seems to have a dash typed in front of the arrowhead. How do I get the arrow drawn correctly - and longer? Currently, the arrowheads of the arrows are drawn directly over the letters "r," "s," and "t."

Is it customary to have the prime typeset under the arrow or beside it when the ray is indicated by a single letter?

\documentclass{article}
\usepackage{amsmath, mathtools, amssymb, amsthm}
\usepackage[dvipsnames]{xcolor}
\usepackage{tikz}
\usetikzlibrary{calc}
\usepackage{scalerel}
  \def\shrinkage{-2.4mu}
  \def\vecsign#1{\rule[1.388\LMex]{\dimexpr#1-2.5pt}{.36\LMpt}%
  \kern-6.0\LMpt\mathchar"017E}
  \def\dvecsign#1{\smash{\stackon[-1.989\LMpt]{\SavedStyle\mkern-\shrinkage\vecsign{#1}}%
  {\rotatebox{180}{$\SavedStyle\mkern-\shrinkage\vecsign{#1}$}}}}
  \def\dvec#1{\ThisStyle{\setbox0=\hbox{$\SavedStyle#1$}%
  \def\useanchorwidth{T}\stackon[-4.2\LMpt]{\SavedStyle#1}{,\dvecsign{\wd0}}}}
  \def\theraysign#1{\rule[1.384\LMex]{\dimexpr#1-2.5pt}{.40\LMpt}%
  \kern-6.0\LMpt\mathchar"017E}
  \def\raysign#1{\smash{\SavedStyle\mkern-\shrinkage\theraysign{#1}}}
  \def\ray#1{\ThisStyle{\setbox0=\hbox{$\SavedStyle#1$}%
  \def\useanchorwidth{T}\stackon[-4.2\LMpt]{\SavedStyle#1}{,\raysign{\wd0}}}}
  \usepackage{stackengine,amsmath}
  \stackMath
  \usepackage{graphicx}
\begin{document}
\begin{center}
\begin{tikzpicture}
%An angle and its angle bisector are drawn.
\path (0,0) coordinate (A');
\path ($(A') +({(3/11)(10)},0)$) coordinate (O') ($(O') +({(3/11)9(3/5)},{(3/11)9(4/5)})$) coordinate (B');
\node[anchor={180-1/2(acos(-3/5))}, inner sep=0, font=\footnotesize] at ($(O') +({(180-1/2*(acos(-3/5)))+180}:0.1)$){$O{\makebox[0pt][l]{\smash{${}^{\prime}$}}}$};
\draw[-latex] (O') -- ($(A')!-0.75cm!(O')$);
\path node[anchor=east, inner sep=0, font=\footnotesize] at ($(A')!-0.85cm!(O')$){$\ray{r{\makebox[0pt][l]{\smash{${}^{\prime}$}}}}$};
\draw[-latex] (O') -- ($(B')!-0.75cm!(O')$);
\path node[anchor={(180-acos(-3/5))+180}, inner sep=0, font=\footnotesize] at ($(B')!-0.75cm!(O')$){$\ray{s{\makebox[0pt][l]{\smash{${}^{\prime}$}}}}$};
\coordinate (C') at ($(O') +({(3/11)(-36/19)},{(3/11)72/19})$);
\draw[-latex, dashed] (O') -- ($(C')!-1cm!(O')$);
\path node[anchor={(180-1/2*(acos(-3/5)))+180}, inner sep=0, font=\footnotesize] at ($($(C')!-1cm!(O')$)!-0.05cm!(O')$){$\ray{t{\makebox[0pt][l]{\smash{${}^{\prime}$}}}}$};
\end{tikzpicture}
\end{center}
\end{document}

Answer 1

The code you've borrowed is for an arrow that can be as long as necessary. Since you only need one letter, I don't quite see why you want that code. The following is four different ways of typesetting the four labels you have in your code. (I've taken the labels out of the TikZ picture, since that was unrelated to what you're trying to do.)

1. Your approach, where the arrows are too close to their letters in footnote size.
2. The TeX defined \vec, where the prime is too close to the vector.
3. \vec, but then using Jasper's suggested \mkern2mu.
4. Using \,, which TeX defines to be \mkern3mu.

Options 3 and 4 look good to me. Note that the preamble is only present for option 1; options 2, 3, and 4 require no preamble at all.

\documentclass{article}
% this entire preample is only necessary for defining \ray
\usepackage{scalerel}
\def\shrinkage{-2.4mu}
\def\vecsign#1{\rule[1.388\LMex]{\dimexpr#1-2.5pt}{.36\LMpt}%
  \kern-6.0\LMpt\mathchar"017E}
\def\dvecsign#1{\smash{\stackon[-1.989\LMpt]{\SavedStyle\mkern-\shrinkage\vecsign{#1}}%
  {\rotatebox{180}{$\SavedStyle\mkern-\shrinkage\vecsign{#1}$}}}}
\def\dvec#1{\ThisStyle{\setbox0=\hbox{$\SavedStyle#1$}%
  \def\useanchorwidth{T}\stackon[-4.2\LMpt]{\SavedStyle#1}{,\dvecsign{\wd0}}}}
\def\theraysign#1{\rule[1.384\LMex]{\dimexpr#1-2.5pt}{.40\LMpt}%
  \kern-6.0\LMpt\mathchar"017E}
\def\raysign#1{\smash{\SavedStyle\mkern-\shrinkage\theraysign{#1}}}
\def\ray#1{\ThisStyle{\setbox0=\hbox{$\SavedStyle#1$}%
  \def\useanchorwidth{T}\stackon[-4.2\LMpt]{\SavedStyle#1}{,\raysign{\wd0}}}}
\usepackage{stackengine}
\stackMath
\begin{document}
\renewcommand{\arraystretch}{1.3}
\begin{tabular}{lll}\hline
& Normal size & Footnote size\\hline
your approach
& $O{\makebox[0pt][l]{\smash{${}^{\prime}$}}}$, $\ray{r{\makebox[0pt][l]{\smash{${}^{\prime}$}}}}$, $\ray{s{\makebox[0pt][l]{\smash{${}^{\prime}$}}}}$, $\ray{t{\makebox[0pt][l]{\smash{${}^{\prime}$}}}}$
& {\footnotesize $O{\makebox[0pt][l]{\smash{${}^{\prime}$}}}$, $\ray{r{\makebox[0pt][l]{\smash{${}^{\prime}$}}}}$, $\ray{s{\makebox[0pt][l]{\smash{${}^{\prime}$}}}}$, $\ray{t{\makebox[0pt][l]{\smash{${}^{\prime}$}}}}$} \
naive approach
& $O'$, $\vec r'$, $\vec s'$, $\vec t'$
& {\footnotesize $O'$, $\vec r'$, $\vec s'$, $\vec t'$} \
Jasper's suggested kern
& $O'$, $\vec r\mkern2mu'$, $\vec s\mkern2mu'$, $\vec t\mkern2mu'$
& {\footnotesize $O'$, $\vec r\mkern2mu'$, $\vec s\mkern2mu'$, $\vec t\mkern2mu'$} \
thinmuskip
& $O'$, $\vec r,'$, $\vec s,'$, $\vec t,'$
& {\footnotesize $O'$, $\vec r,'$, $\vec s,'$, $\vec t,'$} \\hline
\end{tabular}
\end{document}