Should Amazon RHVSA Instances be in same availability zone ??

Issue

That guide states, "The Red Hat VSA is the only way to assure highly available
storage within AWS. Synchronous replication provides redundancy and protection
within a single data center or multiple data centers and availability zones in
a region."

Please reconcile this conflicting information.
I'm creating a new VSA cluster and need to determine whether or not I can do
so in such a manner that our data will survive the failure of a single
availability zone.