adjusting symbols above letter in mathmode

Question

I know there are plenty of similar questions. If you check out the lower picture, you can see that i've tried a bunch of things to solve my problem. That's just one picture...i'm kind of obsessed with the detail here. I've also tried all \smallfrowns and \arrowright commands and they are even uglier. The biggest problem seems to be that the curve above the letter is not proportional to the size of the letter...AND most of the times it's to far away (height). I deleted my solution so please do not ask what commands i have used in my example. That was weeks ago. But if you need some sort of MWE let me know.

However, what i want is a solution like in the first picture.

My documentclass: \documentclass{scrreprt}

in case it makes a difference, i also use: \usepackage{amsmath, amssymb}

Answer 1

Here I offer two variants, where a right paren (rotated) is scaled to the proper width, or where it is stretched to the proper width. The vertical offset is controlled by the optional argument to \stackon. I personally find the \stretchto option superior.

EDIT: Definitions tweaked to auto-handle smaller mathstyles.

\documentclass{article}
\usepackage{stackengine,scalerel,graphicx}
\stackMath
\newcommand\overarc[1]{\ThisStyle{%
  \setbox0=\hbox{$\SavedStyle#1$}%
  \stackon[.5pt]{\SavedStyle#1}{%
  \rotatebox{90}{$\SavedStyle\scaleto{)}{.95\wd0}$}}}}
\begin{document}
\centering
Using \verb|\scaleto|:
\[ \overarc{x} \quad \overarc{X} \quad \overarc{ABC} \]
\[ \frac{F_z}{\overarc{z}}  \frac{F_z}{\scriptstyle\overarc{z}}
  \frac{F_z}{\scriptscriptstyle\overarc{z}} \]

\renewcommand\overarc[1]{\ThisStyle{%
  \setbox0=\hbox{$\SavedStyle#1$}%
  \stackon[.5pt]{\SavedStyle#1}{%
  \rotatebox{90}{$\SavedStyle\stretchto{)}{.95\wd0}$}}}}
Using \verb|\stretchto|:
\[ \overarc{x} \quad \overarc{X} \quad \overarc{ABC} \]
\[ \frac{F_z}{\overarc{z}}  \frac{F_z}{\scriptstyle\overarc{z}}
  \frac{F_z}{\scriptscriptstyle\overarc{z}} \]
\end{document}