As explained in the FAQ, some routers don't push the IP of Pi-Hole for DNS, they push their IP. So, the clients send all their DNS requests to the router, and the router sends them all to the Pi-Hole and the requests appear to originate from the router.
Other routers push the DNS of the Pi-Hole to the clients, and then the clients send their DNS requests directly to the Pi-Hole and Pi-Hole sees individual IP's instead of the IP of the router.
I use Apple routers, and they fall into the second category. In my Pi-Holes, I see the individual IP's of the clients, not the IP of the router for the DNS requests to Pi-Hole.
Since your router falls into the first category, you have several options to change the behavior.
- Use the Pi-Hole as DHCP.
- Manually map clients to the Pi-Hole DNS service.