Customizing the amount of blend between hexes

yes, this it is controlled partially by the size of the "hex sprites" which render to the chunk texture, and then by blending value which calculates distance from hex center and is modified by mixer strenght and hex order at this point. My recomendation would be to try to shrink hex mesh used to render independent hexes, but you need to keep an eye for an artifacts which can occur when hexe textures are too small and non of the three neighbours have coverage in some pixels. When you find sweet point for that I will adjust rest in the shaders.

fastest but less nice solution would be to have very little strenght in the mixer so that distance form hex center is more dominant.