Assigned Client Identifier should be less than 247 bytes

In section 3.5.10, it says:

Informative comment

Assigned Client Identifiers SHOULD be less than 247 bytes so they can be accommodated in a small packet version. This is also to cater for devices which may not support larger Client Identifiers.

But the auth fields can be up to 256 bytes each. Only 36 characters is needed for a UUID, so I think this should be a lot shorter, say 64 bytes?