Vault + Consul storage backend dedicated cluster

I’m in the process of adding a second consul cluster in a datacenter / LAN segment for dedicated Vault storage purposes as referenced in Vault reference architecture
Per the doc above; configuring the gossip / server ports to 7xxx should prevent gossip with the existing cluster; however, after starting and bootstrapping the new consul cluster I’m seeing the new consul servers joining the existing consul cluster.
Short of blocking the traffic is there something I’m missing in the docs?