# An issue with centering

I am trying to include several pages of a pdf within a document (hence using includepdf). These take up most of the page, so a 1-to-1 page input to page output is desired. The main document is two sided with odd and even margins set and some fancy headers. When I include the pdf pages, these are not respecting the page margins (seemingly always centred). How can I get the page margins to be preserved? (I would also like the solution to have the included pdfs vertically centred in the space the text would otherwise fill). I don't want to enforce that the included pages start after a \cleardoublepage, but just a \clearpage.

# Undesired alignment from includepdf

Using the code (as in the MWE)

\includepdf[page={3-4}, frame, trim={30mm 50mm 30mm 50mm}, clip=true, pagecommand={\pagestyle{fancy}},width=\linewidth]{dummy_pages}


# The sort of alignment I want from includegraphics

\noindent
\fbox{\includegraphics[width=\linewidth, page=3, trim={30mm 60mm 30mm 60mm}, clip=true]{dummy_pages}}


The alignment here is better albeit I think the inner margin is still not perfectly aligned despite stating width=\linewidth.

# MWE

I have created a pdf file called dummy_pages.pdf which is dozens of page of lipsum.

\documentclass[a4paper,11pt,twoside]{book}
\usepackage{lipsum}
\usepackage{fancyhdr}
\usepackage{pdfpages}
\usepackage[top=20mm,bottom=20mm,left=20mm, right=30mm, heightrounded, marginparwidth=24mm,  marginparsep=3mm, headsep=10mm]{geometry}

% The nice headers and footers.
\pagestyle{fancy}
% Specifying the headers and footers.
\fancyhf{}
\fancypagestyle{plain}{%
\fancyhf{}%
}
\cfoot{}

\begin{document}
\lipsum
\clearpage

\includepdf[page={3-4}, frame, trim={30mm 50mm 30mm 50mm}, clip=true, pagecommand={\pagestyle{fancy}},width=\linewidth]{dummy_pages}

\end{document}


Here the fancy headers shows the page numbering and margins.

# Related material

There is a related question and answer here to how to position pdf with \includepdf in book, also depending on even/odd page. However, their "solution" is more of a one-off hack than a solution.

Isn't this what offset is for? It adapts automatically to even/odd pages, so you just need half the difference between the inner and outer margins.

\documentclass[a4paper,11pt,twoside]{book}
\usepackage{kantlipsum}
\usepackage{fancyhdr,calc}
\usepackage{pdfpages}
\usepackage[top=20mm,bottom=20mm,left=20mm, right=30mm, heightrounded, marginparwidth=24mm,  marginparsep=3mm, headsep=10mm]{geometry}

% The nice headers and footers.
\pagestyle{fancy}
% Specifying the headers and footers.
\fancyhf{}
\fancypagestyle{plain}{%
\fancyhf{}%