Inherent

The thing that made more logical sense to me is that the Parshendi fought over the gemhearts within the Alethi warcamp range in order to limit the supplies available to the warcamps. Less gemhearts means less soulcasting meaning less food and buildings for the Alethi. If the Parshendi won enough they could force the High Princes to leave the Shattered Plains. On the note of having a forward camp closer to the Alethi War Camps. it has been made abundantly clear that the Parshendi fear the Alethi's brutality and treatment of Parshmen, as well as being heavily outnumbered that putting themselves in a position of danger was not really an option.