The shaded area between Yeep and the coastal Serlits represents not that the area is "contested" so much as that Yeep control of that area is, shall we say, not particularly stable ;-).
A distinction should be drawn between so-called "coastal serlits" and "mountain serlits"...dwelling locations self-evidently different but they don't particularly like each other and have no ethical difficulties in helping greater powers gain land at the others' expense. a short-sighted policy? yes, probably :-).
Mountain Serlit tribes are scattered along the mountains which form the backbone of the island and run approximately from the yeep/serlit/taros junction, following the national boundaries around to about halfway down the unnamed/taros border