FreeBSD legacy license with restrictions on copyright notice placement

[Richard Fontana <rfontana@redhat.com>]

Greetings debian-legal!

I understand Debian includes the package libbsd in Debian main. This
package includes a man page with the following license (see
https://git.hadrons.org/cgit/debian/pkgs/libbsd.git/tree/debian/copyright#n214)

License: BSD-5-clause-Peter-Wemm
 Redistribution and use in source and binary forms, with or without
 modification, is permitted provided that the following conditions
 are met:
 1. Redistributions of source code must retain the above copyright
    notice immediately at the beginning of the file, without modification,
    this list of conditions, and the following disclaimer.
 2. Redistributions in binary form must reproduce the above copyright
    notice, this list of conditions and the following disclaimer in the
    documentation and/or other materials provided with the distribution.
 3. This work was done expressly for inclusion into FreeBSD.  Other use
    is permitted provided this notation is included.
 4. Absolutely no warranty of function or purpose is made by the author
    Peter Wemm.
 5. Modifications may be freely made to this file providing the above
    conditions are met.

I'm curious if there are opinions on why "must retain the above
copyright notice immediately at the beginning of the file" is
consistent with the DFSG. This is one of a variety of 1990s FreeBSD
3-clause BSD variants with such a feature.

Richard