Uneven margins when converting from HTML to Word doc

Consider an HTML document whose contents are simply:

<p>Lorem ipsum dolor sit amet, consectetur adipiscing elit.</p>

i.e. no CSS or style formatting of any kind. When I try to convert it to .doc like this:

soffice --headless -env:UserInstallation=file:///tmp/nonexistent-directory --convert-to 'doc:MS Word 97' document.html

the resulting document has strange margins; 0.79" on the left side, but 0.39" on all others. In contrast, when creating a new blank Writer document in the graphical UI, the margins are 0.79" on all sides.

Why is that? I’m guessing it’s not because of any user settings of mine, partially because I didn’t change any of them from the defaults, and partially because the UserInstallation argument above should force that invocation of it to use a completely blank environment.

Is there any way to specify different margins, like an argument to the conversion command, or a configuration setting, or changing a file template, or something to control the resulting document’s page setup? I’ve been searching but so far I haven’t been able to find anything enlightening in the documentation, or in Google searches, or even looking through the source code.

Version information

Version: / LibreOffice Community
Build ID: 40(Build:1)
CPU threads: 20; OS: Linux 6.1; UI render: default; VCL: gtk3
Locale: en-US (en_US.UTF-8); UI: en-US
Debian package version: 4:7.4.5-2
Calc: threaded