Different inner/outer margins on odd/even pages using Geometry [duplicate]

Question

I'm trying to typeset a book (actually, a dictionary) but keep having trouble setting equal inner and outer margins on both even and odd pages. I have done it numerous times before, but this time either Geometry ignores my parameters or sth else is going on.

I would be grateful if you could shed some light...

Here's what the code looks like (not the complete source):

\documentclass[6pt,twoside]{scrbook}

\usepackage[paperwidth=4.125in, 
            paperheight=6.25in, 
            bindingoffset=0.2in,
            inner=1.0in,
            outer=0.5in,
            top=0.4in,
            bottom=0.75in,
            columnsep=20pt,
            layoutsize={4in,6in},
            layouthoffset=0.125in,
            layoutvoffset=0.25in,
            showcrop=true,
            showframe=true
            ]
            {geometry}

And here's what the result looks like (I would obviously like a greater outer margin on odd pages - and an accordingly smaller inner margin - so that everything fits fine)

P.S. In case it matters, the source code is being compiled with xelatex. If you need to see more code, just let me know! ;)

---

UPDATE

Source sample:

%----------------------------------------------------------------------------------------
% PACKAGES AND OTHER DOCUMENT CONFIGURATIONS
%----------------------------------------------------------------------------------------

\documentclass[6pt,twoside]{scrbook}

\usepackage[paperwidth=4.125in, 
      paperheight=6.25in, 
      bindingoffset=0.2in,
        inner=1.0in,
        outer=0.5in,
        top=0.4in,
        bottom=0.75in,
        columnsep=20pt,
        layoutsize={4in,6in},
        layouthoffset=0.125in,
        layoutvoffset=0.25in,
        showcrop=true,
        showframe=true
      ]
      {geometry}

\usepackage[strict]{changepage}
\usepackage{atveryend}
\usepackage{fontspec}
\defaultfontfeatures{Ligatures=TeX}
\usepackage{palatino}
\usepackage{microtype}

\usepackage{multicol}

\usepackage[bf,sf,center]{titlesec}
\usepackage{afterpage}
%\usepackage{ragged2e}
\usepackage{lipsum}
\usepackage{fancyhdr}
\fancyhead[L]{\textsf{\rightmark}}
\fancyhead[R]{\textsf{\leftmark}}
\fancyfoot[LE,RO]{\thepage}
\fancyfoot[C]{}
\pagestyle{fancy}

%\usepackage[utf8]{inputenc}
%\usepackage[T2A,T1]{fontenc}
\usepackage[spanish,english]{babel}
\usepackage{tikz}
\usetikzlibrary{positioning}
\usetikzlibrary{backgrounds}
\usetikzlibrary{calc}

\definecolor{ultralightgray}{gray}{0.90}

\usepackage{tabularx}

\newcommand{\printchaptertitle}[1]{
\vspace{0.5cm}
\flushleft
\begin{tikzpicture}
  \draw[fill,color=black] (0,0) rectangle (1cm,1cm);
  \draw[color=white] (0.5cm,0.5cm) node { \Huge{#1} };
\end{tikzpicture}
\vspace{0.5cm}
}
\setlength{\parindent}{0pt}
\setmainfont[ItalicFont={Times New Roman Italic},BoldItalicFont={Times New Roman Bold Italic}]{Frutiger}
\setsansfont[ItalicFont={Times New Roman Italic},BoldItalicFont={Times New Roman Bold Italic}]{Frutiger}

\newfontfamily\hebr{Myriad Hebrew}

\usepackage{hang}
\usepackage{xeCJK}
\setCJKmainfont{PingFang SC}
\setCJKsansfont{PingFang SC}

\newcommand{\conjpageindex}[2]{
  \leavevmode\checkoddpage
  \ifoddpage{\begin{tikzpicture}[overlay,remember picture]\node[left,rectangle,white,fill=darkgray!70!white,minimum width=1.4cm,text width=1.0cm,align=left] at ($(current page.east) +(0cm,#2)$){\bfseries{#1}};\end{tikzpicture}}\else{\begin{tikzpicture}[overlay,remember picture]\node[right,rectangle,white,fill=darkgray!70!white,minimum width=1.4cm,text width=1.0cm,align=right] at ($(current page.west) +(0cm,#2)$){\bfseries{#1}};\end{tikzpicture}}\fi
}

\newcommand{\lemmaposp}[1]{{\textcolor{darkgray}{\bfseries\textit{#1}}}}

\newcommand{\lemmagender}[1]{{\textit{#1}}}

\newcommand{\conjsection}[1]{%
  {$\smash{\textbf{\color{black} #1}}$}
}

\newcommand{\conjsubsection}[1]{%
  {\textit{\underline{\smash{#1}}}}
}

\newcommand{\conjseparator}{%
  \vspace{0.3cm}
}

\usepackage{tcolorbox}
\definecolor{mycolor}{rgb}{0.435, 0.435, 0.435}
\makeatletter
\newcommand{\mybox}[1]{%
  \setbox0=\hbox{#1}%
  \setlength{\@tempdima}{\dimexpr\wd0+13pt}%
  \begin{tcolorbox}[colframe=mycolor,boxrule=0.5pt,arc=4pt,
      left=6pt,right=6pt,top=6pt,bottom=6pt,boxsep=0pt,width=\@tempdima]
    #1
  \end{tcolorbox}
}
\makeatother

\begin{document}


%%%%%%%%%%%%%%%%%%%%%%%%%%%%
% PHRASEBOOK
%%%%%%%%%%%%%%%%%%%%%%%%%%%%

\chapter*{Phrasebook}
\addcontentsline{toc}{chapter}{Phrasebook}

\section*{Numbers}
\addcontentsline{toc}{section}{Numbers}

\lipsum[1-12]

\section*{Useful Phrases}
\addcontentsline{toc}{section}{Useful Phrases}

\lipsum[1-12]

\end{document}

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
% This is the end,
% my only friend the end...
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

Answer 1

The following gives a symmetrical layout between odd and even pages:

\documentclass[fontsize=6pt,twoside]{scrbook}

\usepackage[paperwidth=4.125in,
            paperheight=6.25in,
            %bindingoffset=0.2in, %  <----------- commented out
            inner=1.0in,
            outer=1.0in,          %  <----------- same as inner
            top=0.4in,
            bottom=0.75in,
            columnsep=20pt,
            layoutsize={4in,6in},
            layouthoffset=0.125in,
            layoutvoffset=0.25in,
            showcrop=true,
            showframe=true
            ]
            {geometry}

% You can also use this to visualize the layout:
% \usepackage{showframe}
% \renewcommand\ShowFrameLinethickness{0.15pt}
% \renewcommand*\ShowFrameColor{\color{blue!30!white}}

\begin{document}
  \noindent A\newpage \noindent B
\end{document}

---

Note: after seeing the KOMA-Script warning, I replaced your 6pt \documentclass option with fontsize=6pt.