\placefigure[bottom]{}{\externalfigure[hacker][width=\textwidth]}
works just fine,
I get "top" placement with
\placefigure[bottom]{}{\externalfigure[hacker][width=\paperwidth]}

Works here with the code below. The same result with and without adding "force". Result attached.

Do you have an MWE?

\showframe
\starttext
 some text
\placefigure[top]{top textwidth}{\externalfigure[hacker][width=\textwidth]}
 some text
\page
 some text
\placefigure[here]{here textwidth}{\externalfigure[hacker][width=\textwidth]}
 some text
\page
 some text
\placefigure[bottom]{bottom textwidth}{\externalfigure[hacker][width=\textwidth]}
 some text
\page
 some text
\placefigure[top,force]{top force paperwidth}{\externalfigure[hacker][width=\paperwidth]}
 some text
\page
 some text
\placefigure[here,force]{here force paperwidth}{\externalfigure[hacker][width=\paperwidth]}
 some text
\page
 some text
\placefigure[bottom,force]{bottom force paperwidth}{\externalfigure[hacker][width=\paperwidth]}\stopmode
 some text
\page
 some text
\placefigure[top]{top paperwidth}{\externalfigure[hacker][width=\paperwidth]}
 some text
\page
 some text
\placefigure[here]{here paperwidth}{\externalfigure[hacker][width=\paperwidth]}
 some text
\page
 some text
\placefigure[bottom]{bottom paperwidth}{\externalfigure[hacker][width=\paperwidth]}
 some text
\stoptext

--
Rik