Remove blank vertical space between Sender/Recipient in LaTeX letter package scrlttr2

Question

I am constructing a letter using the scrlttr2 package.

I've dived through a lot of questions about how to handle the sizes of the Sender Recipient section (at the top of just the first page). Using the geometry package doesn't work, as it does not affect the sender and recipient text boxes, just the body text. However, I couldn't get a solution to the issue. I found the scrlttr2 package here, but there is no way 'pseudo-length' (page 166) to reduce the white space between the sender and recipient.

I want to reduce this space:

Here is my code, the sender info is in a file sender.lco:

\documentclass[
    sender,
    paper=a4,
    version=last,
    firstfoot=false,
    fontsize=10pt,
    DIV=13,
    BCOR=0mm]{scrlttr2}
\parskip3mm
\parindent5mm 
\usepackage[english,ngerman]{babel}
\usepackage[utf8]{inputenc}
\usepackage{csquotes}

\usepackage{lmodern}
\renewcommand*\familydefault{\sfdefault}
\usepackage[T1]{fontenc}

\usepackage{changepage}

\changepage{1cm}{0cm}{-1cm}{0cm}{0cm}{0cm}{0cm}{0cm}{0cm}

\begin{document}


\setkomavar{subject}{Reference: Letter }
\setkomavar{date}{ \today}
\setkomavar{place}{XXX}

\setplength[]{baselineskip}{0.25cm}

% Set recipient of letter
\begin{letter}{
    \textbf{TO}:  
XXX\\
XXX\\
XXX
}
\opening{To whom it may concern,}

% Write here your Letter text. You can choose here the language for typeset. ("english", or "ngerman")
\selectlanguage{english}

Body texttttttttttttttttt

\closing{Respectfully Yours,} % use "Mit freundlich Grüßen" i.e. 
\end{letter}

\end{document}

Answer 1

You could use

\LoadLetterOption{visualize}
\showfields{head,address,refline}

to visualize the positions of first head, address field and refline (only the date in your example).

Maybe you simple want to load letter class option DINmtext.lco:

\documentclass[
    %sender,% there is no sender.lco given in the question
    paper=a4,
    version=last,
    firstfoot=false,
    enlargefirstpage,% <- added
    fontsize=10pt,
    DIV=13,
    BCOR=0mm,
    DINmtext
    ]{scrlttr2}
\setkomavar{fromname}{Max Mustermann}% <- added
\setkomavar{fromaddress}{YYY\\YYY}%<- added

\usepackage[T1]{fontenc}
%\usepackage[utf8]{inputenc}% needed with old (outdated) TeX distributions
\usepackage[english,ngerman]{babel}
\usepackage{csquotes}
\usepackage{lmodern}

\setparsizes{3mm}{5mm}{0pt plus 1fil}% par skip 3mm, par indent 5mm
\renewcommand*\familydefault{\sfdefault}

%\usepackage{changepage}
%\changepage{1cm}{0cm}{-1cm}{0cm}{0cm}{0cm}{0cm}{0cm}{0cm}

\usepackage{blindtext}% only for dummy text
% visualize positions of head, address, refline in the example:
\LoadLetterOption{visualize}
\showfields{head,address,refline}

\begin{document}
%\setplength[]{baselineskip}{0.25cm}% undefined

\begin{letter}{
    \textbf{TO}:  
XXX\\
XXX\\
XXX
}
\setkomavar{subject}{Reference: Letter }
\setkomavar{date}{ \today}
\setkomavar{place}{XXX}
\selectlanguage{english}
\opening{To whom it may concern,}
\Blindtext[2]
\closing{Respectfully Yours,} % use "Mit freundlich Grüßen" i.e. 
\end{letter}
\end{document}

---

Disclaimer: I would neither change the position of address field and/or refline (date) nor the size of the address field. If you do so, you can not use a window enlovpe.

But it is possible to adjust the vertical position of address field and refline, if you really want to do so. But then ia. the back address in the address field is useless.

\documentclass[
    %sender,% there is no sender.lco given in the question
    paper=a4,
    version=last,
    firstfoot=false,
    enlargefirstpage,% <- added
    fontsize=10pt,
    DIV=13,
    BCOR=0mm,
    addrfield=topaligned,% <- added: top align address in address field
    backaddress=false% <- added: back address is useless, if the position of address field is changed
    ]{scrlttr2}
\setkomavar{fromname}{Max Mustermann}% <- added
\setkomavar{fromaddress}{YYY\\YYY}%<- added

\usepackage[T1]{fontenc}
%\usepackage[utf8]{inputenc}% needed with old (outdated) TeX distributions
\usepackage[english,ngerman]{babel}
\usepackage{csquotes}
\usepackage{lmodern}

\setparsizes{3mm}{5mm}{0pt plus 1fil}% par skip 3mm, par indent 5mm
\renewcommand*\familydefault{\sfdefault}

%\usepackage{changepage}
%\changepage{1cm}{0cm}{-1cm}{0cm}{0cm}{0cm}{0cm}{0cm}{0cm}

\setplength{toaddrvpos}{\useplength{firstheadvpos}}
\addtoplength{toaddrvpos}{5\baselineskip}% adjust height reserved for first page header plus vertical sep before address field

\setplength{backaddrheight}{0pt}% remove space for backaddress
\setplength{toaddrheight}{5\baselineskip}% adjust height reserved for address

\setplength{refvpos}{\useplength{toaddrvpos}}
\addtoplength{refvpos}{\useplength{toaddrheight}}
\addtoplength{refvpos}{\baselineskip}% adjust sep between address field and refline


\usepackage{blindtext}% only for dummy text
% visualize positions of head, address, refline in the example:
\LoadLetterOption{visualize}
\showfields{head,address,refline}

\begin{document}
%\setplength[]{baselineskip}{0.25cm}% undefined

\begin{letter}{
    \textbf{TO}:  
XXX\\
XXX\\
XXX
}
\setkomavar{subject}{Reference: Letter }
\setkomavar{date}{ \today}
\setkomavar{place}{XXX}
\selectlanguage{english}
\opening{To whom it may concern,}
\Blindtext[2]
\closing{Respectfully Yours,} % use "Mit freundlich Grüßen" i.e. 
\end{letter}
\end{document}