If I had to guess, the container station might be giving the docker container a new network/ip address, one that the NAS is not using so that port 443 works and doesn't conflict with the NAS. If you start the container station then inspect the container you might see how they do it, but macvlan is typically how you would configure it.
services:
my-lan-service:
image: nginx:latest
container_name: lan_container
# 1. Attach the service to the custom macvlan network
networks:
lan_network:
ipv4_address: 192.168.1.200 # The dedicated LAN IP for this container
# 2. Ports are exposed directly to the LAN; do NOT use the "ports" block
restart: unless-stopped
networks:
lan_network:
driver: macvlan
driver_opts:
parent: eth0 # Change to your host's physical network interface name
ipam:
config:
- subnet: 192.168.1.0/24 # Matches your physical local network setup
gateway: 192.168.1.1 # Your physical router IP
Most of these backup solutions try to reduce the amount of data backed up, so the system will process each file and determine if the contents changed and only upload new data. In this case if you modify the file you may end up with 2 16 MB chunks that have slightly different data, and only when the old backup expires and the pruning process completes would one of those chunks be deleted.
Smaller chunks sizes means you get more files written to S3, but less duplicate data when deduping without compression.