Scale out elastic search

Hi

We are designing our search cluster among regions - namely we will have core (US) and edge regions(US, AU, EU etc). We want the core to host primary nodes of the shards and rest regions to host replica of it.

We have found the following option regarding shard allocation awareness and have tested with two regions -the result is that one regions is hosting primary nodes of the shards and other is hosting the replica.The configuration is default - 5 shards and 1 replica.

cluster.routing.allocation.awarness.attribues

Our problem is that we cannot bind the primary nodes of the shards to be in US core and replica in other region e.g. AU. Is there any other option or way to achieve the goal?

Thanks
Ripon