Come on wildcard. If I wanted to play on a crossark cluster, I'd play on a crossark cluster. Please don't ruin small tribes by makin it a crossark cluster.
What you need to do is make tribe formation count for all of the small tribe servers. For example, if I joined a tribe on server 56, when I transfer to server 24 I should still be in the same tribe of 6 guys that I was in on 56. This will keep the game competitive with cross server raiding but limit mega tribe abuse.
Clustering off small tribe servers is dumb. People play PVP because there is the additional challenge of getting wiped by another tribe. If people can't handle it then they should go play PVE.
The clustering of small tribe servers feels like a liberal knee-jerk reaction. Overly empathetic and ultimately in the wrong direction.
"one of the concerns we've seen is transfers.", they say but they're wrong. Transfers aren't the concern. Mega tribes are the concern. You've not only incorrectly recognized the problem, you've made corrections that are going to only exacerbate the problem or kill server population.