Can residential Xfinity Internet be provisioned with a /60 IPv6 delegated prefix instead of a /64?

Hello,

I'm a residential Xfinity Internet customer in Minnesota using my own DOCSIS modem (Arris SB8200) and a router that supports native IPv6 using DHCPv6 Prefix Delegation.

Recently, after some apparent network maintenance in my area, both my IPv4 address and my IPv6 delegated prefix have changed twice within a short period. Everything is working correctly again, but it prompted me to look more closely at my IPv6 configuration.

Currently, Comcast is delegating a /64 IPv6 prefix to my router. From what I've been able to learn, many advanced routers are designed to work best with a /60 (or larger) delegated prefix because it allows the router to create multiple standard /64 LANs internally, which is how IPv6 was designed to operate.

I'm not trying to obtain additional public IPv4 addresses or business-class service. This is simply a question about IPv6 prefix delegation for a residential customer.

My questions are:

1. Is it possible for a residential Xfinity Internet account to be provisioned with a /60 DHCPv6 delegated prefix instead of a /64?
2. If so, is that something that can be requested for an individual account, or is the delegated prefix size fixed by the network serving my area?

Thank you for any information you can provide.