What is the best way to control the softness of the blending between landscape layers?
A height lerp will give you the best blend, but costs more than a standard lerp. It also requires one of the textures to have a heightmap channel. Based on that alpha, you can more or less begin to “fill” the lower areas(black) first and slowly work towards the top(white), until you reach full saturation; based on a 0 to 1 lerp value.