In IPv6 the first 64 bits are network address, and then the next 64 bits are host address.
Each site should get a /56 at the minimum, this lets you set up 64-56=8 bits worth of subnets, that's 256 subnets.
Instead, ISPs give out a single /64 and it gets put on the WAN subnet, so it's just enough for the router itself to get on the network. The relay mode attempts to "fix" his but it's really just a hack, like when you order a truckload of bricks and they come with an enormous truck and give you one brick... if you went off and made your own bricks instead of complaining that they didn't provide what they said they would.
The smallest recommended prefix is /56, and if your ISP doesn't give out at least /60 it's an indication they haven't got a clue.