Use the docdir given to configure with the --docdir flag.
--- Makefile.in.orig	2008-07-07 15:55:29.000000000 -0500
+++ Makefile.in	2023-09-04 11:47:40.000000000 -0500
@@ -11,7 +11,7 @@
 bindir = @bindir@
 mandir = @mandir@
 man1dir = $(mandir)/man1
-docdir = $(prefix)/doc/sitecopy
+docdir = @docdir@
 localedir = $(datadir)/locale
 datadir = @datadir@
 datarootdir = @datarootdir@