I have built games/cowsay in my own poudriere. In the manpage, it says:
/wrkdirs/usr/ports/games/cowsay/work/stage/usr/local/share/cows holds a
sample set of cowfiles. If your COWPATH is not explicitly set, it
automatically contains this directory.
Notice that the stagedir from building has leaked into the manpage. And if I build the port as a user in /tmp/port, and look at the staged manpage at /tmp/port/work/stage/usr/local/man/man1/cowsay.1.gz, then I see this:
holds a sample set of cowfiles. If your
.. and while the script explicitly handles a "normal" (or maybe "old-fashioned, before staging was a thing") prefix, it substitutes a full prefix (with staging, it seems) in to the intermediate perl scripts -- and onwards into the manpages:
echo s,%PREFIX%,$PREFIX,\; >> install.pl