Setting \textwidth when using newlfm

I want to set the width of the text in a letter that uses the newlfm package. Take the following basic example:

\documentclass[a4paper,12pt]{newlfm}
\usepackage[english]{babel}
\usepackage[utf8]{inputenc}

\setlength{\textwidth}{2cm}

\begin{document}
\begin{newlfm}

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\end{newlfm}
\end{document}


The width of the text is not set to 2cm. But if \begin{newlfm} and \end{newlfm} are removed the width of the text is set to 2cm. But since I want to use newlfm to format my letter removing those commands doesn't solve the issue properly.

I have read the newlfm manual [1] to my best but have been unable to find a solution to this issue.

\newlfmP{textwidthsize=2cm}