Book geometry with margins and binding offset

Question

The mwe given below illustrates my current settings in the book am working. Unfortunately I find it a bit cumbersome and outdated although it achieves what I want it to do. One of my objectives is to have both even and odd pages have the margin on the left side; this has been done. My issue is that I don't think the spacing are the same for both pages. For example, for page 2, the binding is on the right and on 3 it is on the left and showframe does not show the margin paragraph section.

What I want is that all lengths are accounted for and that both pages are technically the same. I feel like I am forcing the geometry to look like what I want.

\documentclass[11pt,twoside,openany]{book}
\usepackage[
    letterpaper,
    bindingoffset=0.2in,
    centering,
    marginparwidth=2in,
    textwidth=5.1in,
    marginparsep=2em,
    top=2.5cm,
    bottom=2cm,
    showframe
]{geometry} 
\evensidemargin 1.5in
\oddsidemargin 2in 

\usepackage{etoolbox}

\makeatletter
\patchcmd{\@mn@margintest}{\@tempswafalse}{\@tempswatrue}{}{}
\patchcmd{\@mn@margintest}{\@tempswafalse}{\@tempswatrue}{}{}
\reversemarginpar
\makeatother

\usepackage{lipsum}
\begin{document}
\lipsum[1-12]
\end{document}

Here is an example of what I would like to achieve and the link to the sample.

The image below gives an overview of the layout I am seeking to achieve.

Answer 1

The different values for \evensidemargin and \oddsidemargin seem questionable to me if you're trying to have a two-sided document have exactly the same off-centred layout.

I'm not sure what you mean by 'margin paragraph section', but if you mean you want the \marginpars to end up always on the left-hand side of both the recto and verso pages, then maybe the following works. (\marginpars can be frustrating to work with.)

\documentclass[11pt,twoside,openany]{book}
\usepackage[
    letterpaper,
    bindingoffset=0.2in,
    centering,
    marginparwidth=2in,
    textwidth=5.1in,
    marginparsep=2em,
    top=2.5cm,
    bottom=2cm,
    showframe
]{geometry}
\evensidemargin 1.5in
\oddsidemargin 1.5in

\usepackage{etoolbox}

\makeatletter
\patchcmd{\@mn@margintest}{\@tempswafalse}{\@tempswatrue}{}{}
\patchcmd{\@mn@margintest}{\@tempswafalse}{\@tempswatrue}{}{}
%\reversemarginpar
\makeatother

\usepackage{ifoddpage}
\newcommand\mmp[1]{%
  \checkoddpage
  \ifoddpage
   \reversemarginpar
   \marginpar[#1]{}
  \else
   \normalmarginpar
   \marginpar{#1}
  \fi
}

\usepackage{lipsum}
\begin{document}
\mmp{Odd, left-hand side}
\lipsum[1-6]
\mmp{Even, left-hand side}
\lipsum[7-12]
\mmp{Odd again, left-hand side}
\end{document}

Answer 2

Using geometry you only need a oneside document and set lmargin, rmargin, marginparwidth and marginparsep options. Of course, enabling \reversemarginpar if you want margin notes in the right (left) margin.

\documentclass[11pt,letterpaper,oneside,openany]{book}
\usepackage[lmargin=8cm,rmargin=1cm,marginparwidth=6cm,marginparsep=2em]{geometry} 
\usepackage{lipsum,sidenotes,tabularx}
\reversemarginpar
\usepackage{graphicx}
\begin{document}
\lipsum[1]\sidenote{A side note text} 
\lipsum[5]
\begin{marginfigure}
\centering
\includegraphics[width=\linewidth]{example-image-a}
\caption{Some image}
\end{marginfigure}
\lipsum[2-5]
\begin{margintable}
\centering
\begin{tabularx}{\linewidth}{|XXXXXX|}
\hline
    11 & 12 & 13 & 14 & 15 & 16\\
    21 & 22 & 23 & 24 & 25 & 26\\
    31 & 32 & 33 & 34 & 35 & 36\\
    41 & 42 & 43 & 44 & 45 & 46\\
    51 & 52 & 53 & 54 & 55 & 56\\
\hline
\end{tabularx}
\caption{Some table}    
\end{margintable}
\lipsum[4-6]
\end{document}

BTW: Taking into account the layout, consider use the tufte-book document class.