fancyhdr 的右边距

Question

使用 fancyhdr 和 onehalfspacing 时如何获得正确的边距？我目前正在写论文，我不太确定我的边距是否正确。这是一个示例代码

\documentclass[12pt,a4paper,twoside,
%     DIV=calc 
     ]{scrreprt}
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

\usepackage[ngerman]{babel}
\usepackage[utf8]{inputenc}
\usepackage[T1]{fontenc}
\usepackage[style=alphabetic]{biblatex}
\usepackage{blindtext}
\usepackage{setspace}
%\KOMAoptions{DIV=last}

\usepackage{fancyhdr}
\pagestyle{fancy}
%\KOMAoptions{DIV=last}

\parindent0pt

\renewcommand{\chaptermark}[1]
{\markboth{\MakeUppercase{
 \thechapter.\ #1}}{}}
\renewcommand{\sectionmark}[1]
{\markright{\MakeUppercase{\thesection\ #1}}{}}

\fancyhead[L]{ \leftmark \text{}}
\fancyhead[R]{{\rightmark}}
\fancyfoot[C]{\thepage}

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

\raggedbottom
\begin{document}
\onehalfspacing
\chapter{introduction}
\blindtext
\blindtext
\blindtext
\end{document}

我觉得编译后的版本边距非常小。我尝试通过添加 进行调整DIV=calc，但边距似乎太大了。

哪一个是正确的方法？也许有人知道边距应该有多大。

非常感谢！