Thanks for posting on our forum!
As you found out, rack-aware is currently only in place for replication factor 2. It is just not implemented for higher replication factors. So, it is only for the more basic and trivial use case of replication factor 2 that the feature is in place, where we have to make sure that for each partition the master and replica copies are on 2 nodes in different racks.
In general though, we do recommend setting up clusters with nodes as close to each other as possible to ensure highest stability when it comes to the vital heartbeat traffic between the nodes. Failure cases would then be covered by setting up a second cluster and our XDR component for replicating data to it.