I believe what the OP really wants (and I agree with) is a mechanism in place to deter very large clans from easily controlling large swaths of land.
Think about it. If there is no downside to owning more tribal land, then it the largest clans can and will take over as much as the game lets them.
There needs to be a downside. It could be in the form of no instant travel so it becomes more difficult to defend all of your holdings the more you spread out. Upkeep would also deter this from happening.
For those worried about an additional timesink - the upkeep could be scaled up nonlinearly depending on how much land the tribe controls.