How does a figure's height influence its positioning?

Sometimes a figure I want to place at the bottom of a page is placed on the next page regardless of the available space. I, finally, did some testing and realized that the height of a figure may not be more than 25% of the textheight for it to be placed at the bottom. And, at least in my tests, it may not exceed 65% of the textheight to be placed at the top.

UPDATE:
As described by the comments and the linked explanation of the placing algorithm in most cases adding ! to the positioning parameters should solve the problem. Following a working example with bottom positioning and a page of follow-up text:

documentclass{article}
usepackage{graphicx}
usepackage{lipsum}
begin{document}

Some text here.

begin{figure}[!b]%
includegraphics[draft, height=0.40textheight, width=0.6columnwidth]{example-image}%
centering
caption{Relaxing constraints with !, this figure (40% textheight) 
    will be placed at the bottom, too.}%
label{}%
end{figure}

lipsum[1-5]

end{document}

However, in my original document, the text and figure is followed by a minipage which does not fit into the same page and needs to be placed on the next page (in fact, it is a rather lengthy lstlisting which I don’t want to break up). Adding such a minipage to the above code yields strange behavior. The figure is placed on the first page but not at the bottom. Instead it seems to behave as if the h positioning has been used:

documentclass{article}
usepackage{graphicx}
usepackage{lipsum}
begin{document}

Some text here.

begin{figure}[!b]%
includegraphics[draft, height=0.40textheight, width=0.6columnwidth]{example-image}%
centering
caption{Relaxing constraints with !, this figure (40% textheight) 
    will be placed at the bottom, too.}%
end{figure}

begin{minipage}{linewidth}
lipsum[1-5]
end{minipage}

end{document}

The same behavior can be observed when I add the text without a minipage but trigger a pagebreak before the lipsum. I assume minipage may introduce a pagebreak or equivalent if it doesn’t fit onto a page.

Last but not least, a clearpage before the minipage solves the problem and places the figure at the bottom while, as far as I understand the algorithm, a figure may only be placed on subsequent pages when the layouter reaches a clearpage:

documentclass{article}
usepackage{graphicx}
usepackage{lipsum}
begin{document}

Some text here.

begin{figure}[!b]%
includegraphics[draft, height=0.40textheight, width=0.6columnwidth]{example-image}%
centering
caption{Relaxing constraints with !, this figure (40% textheight) 
    will be placed at the bottom, too.}%
label{}%
end{figure}

clearpage
begin{minipage}{linewidth}
lipsum[1-5]
end{minipage}

end{document}

I love such corner cases as I constantly seem to run into them in every aspect of my life. Maybe someone can explain what happens here and how to deal with the situation in a way which does not fall back on you ten pages later in the document 😉

Best wishes,
Stefan