OK, the real issue here is with the amount of regions a player must conquer in order to get his first bonus.
Huli - 2
Iwan - 3
Motu - 4
Jiwiki - 4
Chimbu - 4
Enga - 3
Highland - 3
Asaro - 3
--> Huli would very probably get their +2 bonus in a second turn and then could damage other players, gaining a massive advantage, while in speedier games Chimbu would probably never achieve their own bonus.
Optimally, these number should all be the same, probably 3 (therefore 4 regions for the whole bonus zone);
so, for example,
Huli - either make a new territory between Saraga and Jacksons OR Saraga and Faiv Mail
Motu - merge Paga and Lapun Biktaun
Jiwiki - merge Napa Napa Rot Fo and Napa Napa Rot Tre
Chimbu - merge Gogodala Viles and Baruni Westim Ples
-> the bonuses then should be changed accordingly.
((Alternatively, I am thinking about more complicated gameplay tweaks - such as giving only a maximum of +1 bonus per a minimum of 2 regions in the bonus area close to the tribe IF the player holds the tribe.
That would also reduce any possible early game advantages/disadvantages for getting a strong bonus zone & being lucky in your first turn. I am fairly confident that XML would allow this, but I think it is rather complicated, so I'd rather try to balance it out by redrawing as I suggested above.))