DCHP reserve limit

Hi

I have a RAX200 router. Im looking to create reserved IP addresses. However it seems I can only add 3 in total? Is that right?

I go to add a new reserved address, pick a device from the list and give it an IP. The first 4 add no problem. But when you add any more it just replaces the 3rd one with your new device.

Surely that's not right in a £400+ router? On other cheaper routers I'm can easily reserve 100 addresses.

Is this a limitation with this router or am I doing something wrong????