Debian installation automation?

Question

Debian

Good day!
I'm trying to determine the local package repository through preseed. I can't get a line with "volatile" packages added to the sources.list of the installed system.
preseed lines:

d-i mirror/protocol string http
d-i mirror/country string manual
d-i mirror/http/hostname string 192.168.1.10
d-i mirror/http/directory string /deb.debian.org/debian
d-i apt-setup/security_host string 192.168.1.10/security.debian.org
d-i apt-setup/volatile_host string 192.168.1.10/deb.debian.org/debian
d-i apt-setup/services-select multi-select volatile, security
d-i mirror/http/proxy string
d-i apt-setup/non-free boolean true
d-i apt-setup/contrib boolean true
d-i apt-setup/enable-source-repositories boolean false

The contents of sources.list on the installed system:

# deb http://192.168.1.10/deb.debian.org/debian stretch main
deb http://192.168.1.10/deb.debian.org/debian stretch main non-free contrib
# deb-src http://192.168.1.10/deb.debian.org/debian stretch main non-free contrib
deb http://192.168.1.10/security.debian.org/debian-security stretch/updates main contrib non-free
# deb-src http://192.168.1.10/security.debian.org/debian-security stretch/updates main contrib non-free

Accordingly, the line

deb http://192.168.1.10/deb.debian.org/debian/ stretch-updates main contrib non-free

is absent.
What other preseed settings can be used to make this line appear in sources.list?

Answer 1

Only adding to the preseed line helped

d-i apt-setup/local0/repository string deb http://192.168.1.10/deb.debian.org/debian/ stretch-updates main contrib non-free

Although I think that this is not quite the right approach.