Float overlaps due to low value of \textfraction?

Question

In some sources a low value of \textfraction=0.07 is recommmended (see https://aty.sdsu.edu/bibliog/latex/floats.html). However, if I apply these values, some of my floats (both images and tables) overlap with the text, even though there would be enough space. Why is that?

Minimal working example see below:

% Document class
\documentclass[ a5paper, % type of paper
                fontsize=9pt, 
                parskip=half, % distance between paragraphs shall be half a line
                usegeometry, % facilitates use of geometry package into scrbook class
                ]{scrbook}
\usepackage[english, ngerman]{babel}

\usepackage{geometry}
\newgeometry{left=5cm, right=1.6cm, top=1.1cm, bottom=1.1cm, % margins from page to body
    includeheadfoot, % header and footer are considered as part of the body, hence are placed within margins
    headsep=0.6cm, % vertical distance from top of textbody to bottom of header
    footskip=0.9cm, % vertical distance from bottom of textbody to top(?) of footer
    footnotesep=0.9cm, % vertical distance from bottom of textbody to top(?) of footnotes
}
\usepackage{showframe}

\renewcommand{\textfraction}{0.07}  % allow minimal text w. figs
\usepackage[draft]{pgf}


\begin{document}

and classified correctly. Then, the linear fit described in step three can be correctly performed (see right hand side of Fig.~\ref{fig:06_FSM_preoptim}).

\begin{figure} [htbp]
    \centering
    \begin{pgfpicture}
        \pgftext{\pgfimage[width=\textwidth,height=12.927cm]{dummy}}
    \end{pgfpicture}
    \caption{Diagram, in which the benefits of the preoptimization before the linear fit are demonstrated}
    \label{fig:06_FSM_preoptim}
\end{figure}

\section{Next section}

In contrast to ...

\end{document}

Result is the following:

Answer 1

I don't think the text-image overlap issue you're encountering is related -- at least not immediately -- to the directive

\renewcommand{\textfraction}{0.07}

Instead, it looks like there's a hidden conflict between what the \geometry directive does and what some of the other set-up processes associated with the scrbook class are meant to accomplish. For sure, removing the option

includeheadfoot

from the \geometry directive gets rid of the overlap issue.

I'm afraid that not knowing exactly what the page layout is supposed to be, I can't make other suggestions.

Answer 2

So the issue seems to be a combination of parskip, flushbottom and a significantly underfull vbox. In this case Tex may position elements such that they overlap. This error is known since 2010, but there does not seem to be a general solution instead to manually add a \vspace{\parskip} between the float and the next section heading.

Sources:

• My question in German answered by Markus Kohm: https://komascript.de/node/2176
• Same issue: parskip=half garbles sometimes pages
• Issue explained and solution: https://www.latex-project.org/cgi-bin/ltxbugs2html?pr=latex/4112