Sorry I missuderstood.
Well same problem.
Tribe A vs Tribe C.
Tribe A has 30 people attacking Tribe C at 30 people.
Best thing for Tribe C to do is make Tribe D with 19 members and leave 1 member in Tribe C.
Now Tribe D defends Tribe C's area at 10k% - 300% instead of 10k% - 6000%
So even big clans can act like little ones, and get past the offline issue.
Sorta of a good idea, but still not right. I agree you can do something like this but still the key comes in rewarding people to be allies, but also punishing them with some type of resource used or something.